One thing I've understood about the Axe FX III is that you can play 2 (or more?!) guitars through it at the same time, which is an awesome feature if you want to save space in the live rig.
Will Axe FX IV support 3 instruments? 
You could then cater for 95 % of bands, since they usually have 2 guitars and 1 bass.
Just my 2c, but I had that ESI interface. It's now in the garbage.
It gave me blue screens and crashes every second time I connected it to the computer, YMMV etc.
I've heard the same, but so far so good And as I noticed, it is the only device like that that I could find 
Of course, it's a bit special use case, since I already had an interface prior. Of course, if you are in the market for a new main interface, then it makes sense to just buy an interface that does have the SPDIF I/O built-in. The cheapest such is the Focusrite 6i6, but it doesn't have the best sound quality for other things like mics. The proper devices would be closer to 500+ range.
it also featured direct monitoring. Well, turns out this is only for analog inputs
Couldn't you monitor from the Kemper headphone out? Or if want the backing tracks also, then you could either get the master out from the DAW, or setup a separate monitor mix with whatever tracks you need (eg. drums-only).
thanx alot, I have the audient id14 too, and have been looking for a reamping solution
edit: ..seems it's been around since 2008...
2003 
Edit: Ah, you mean the U24XL. Yup. 2008, and ASIO4ALL since 2003.
Great post thanks. Any drawbacks when using asio4all?
Well, it is of course a 3rd party thing, so it might not work with all devices and could be unstable. But usually it works for most people, since it's been around for 15 years.
Hmm, seems I cannot post images. It just gives a "Message too long" error. Let's see how I can get the images.
Edit:
Linked the images to my webserver.
I was in the situation where I wanted to reamp using SPDIF with the Kemper, but my interface only has a digital INPUT and with Toslink connector to begin with. Unfortunately having only an Input (or only an output) makes reamping impossible since that is a two-way operation. You need both an Input and Output. Also, the Kemper uses RCA plugs for the SPDIF
So, what to do? Well, luckily there is at least ONE (I didn't find any others! 
) device that makes it possible from a hardware point of view, without you needing to spend hundreds on a new interface.
ESI U24 XL, which is about 90 euros (100 USD). It uses USB to transfer the data from SPDIF to your DAW: https://www.esi-audio.com/products/u24xl/
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Handy little piece! But, unfortunately that is not enough. You most likely already have a decent audio interface, or would rather use a different device for playback and recording (other than the reamp).
ASIO4ALL to the rescue! 
http://www.asio4all.org/
Among other things that it is more known for (low latency for less-optimal audio devices), it has the critical little feature we will need to use SPDIF for reamping while using your main interface for everything else.
In ASIO4ALL, you can merge arbitrary ASIO devices into one virtual device. This is because in every DAW, you can only use ONE ASIO device at any given moment. So beyond switching cables back and forth with your main interface and the U24XL, you need a better solution. And that is the virtual device you can "build" with ASIO4ALL. You basically select which Inputs and Outputs you want to include in the virtual device - for example Input 1, Input 2, Output 1 and Output 2 from your main interface, and then the SPDIF Input/Output from the U24XL:
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Here I have activated the Output 1/2 (stereo), Input 3/4, and Input 1/2 from my main interface (Audient iD14), and the Input and Output from the U24XL.
Here are the settings in my U24XL - the critical things are to pick "Digital" and 44100 Hz which the Kemper uses:
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Now when you open your DAW, you will pick the ASIO device called "ASIO4ALL v2" instead of your main one:
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Then comes the important part. Add a new MONO Input source to your DAW, and select the RIGHT side channel (= U24XL 2) instead of left as the input.
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And then, equally important, add a new STEREO Output, which you can call Reamp out for example. Assign channel 1 (U24XL 1) to the Left side, and channel 2 (U24XL 2) to the Right side:
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And on your Kemper,
1) press Input, and make sure the Input Source is "SPDIF Input Reamp"
2) press Output, and make sure the SPDIF Output is "Git / Master Mono" (or if you haven't updated to v5.5, it is called "Git / Master Left" (I think...)
You might also check on Page 5 of the Output settings that SPDIF Clock is at 44.1 kHz
And now... drumroll... we can start reamping! 
1) On your DI track, select the output as Reamp Output (the one that sends to U24XL 1 and U24XL 2 in output settings)
2) Then create a second audio track, and select the Mono input (U24XL 2) as the input source.
3) Arm the audio track for recording, and start recording. It will start to write the signal to the audio track 
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And if you are unfamilar with reamping - yes, you need to record in real time. If you have 4 tracks of guitars and the song is 4 minutes, doing a complete reamping will take at least 4 * 4 = 16 minutes. You might move all 4 tracks one after another to record in one go instead of track by track.
Using an overdrive pedal with the gain at almost zero and volume at almost max is a very common way to tighten up most tube amps.
Sounds cool. Which profile did you use?
For guitars, I used the "CORPSE" preset from Deadlight (Mesa Recto) and for bass I used the "Smashing Fuzz" preset by Ruppert. But there's a bunch of post-processing on them (EQ, some mild multiband comp), and the bass especially is only like 20 % of the Kemper. I took a DI signal also and applied most of the processing on that.
Just for fun, I recorded a cover song and did it with just two rhythm guitar tracks, unlike my usual quad.
You can get a decently thick tone, but you gotta use a very thick sound and boost the bass guitar (volume & distortion) a bit more than usual, to get the thickness:
Oh and Youtube being Youtube, here's a FLAC version too:
http://juhau.mbnet.fi/fearfactory-bodyhammer.flac
Recording primarily the bass DI is the most common method among every studio guy I've chatted with. Most do also record a wet signal, but only use it for some extra tone sometimes.
This seems to be favoured:
DI bass track with no sound
├ (send, prefade) Lowpassed @ 350 Hz, and compressed to flatter than flat
├ (send, prefade) Highpass @ 500 Hz, sometimes lowpassed at 1-2 kHz, and then a crunchy distortion is applied
└ [sometimes] (send, prefade) Highpass @ 1-2 kHz, and then a wide chorus is applied. Sometimes with a fuzzy heavy distortion before the chorus
It creates a basstone that is thick and well defined, but still has some "action" from the higher distortion.
The chorus in the highpassed signal is something I really enjoy too. It magically makes the bass really stand out without drowning anything out. One of my favourite tricks!
Of course, you could replace the highpassed sends with the wet signal from an amp/kemper, which is also highpassed around 500 Hz.
It's a common practice to do mono summing during mixing to check how it sounds in mono. In fact, many (including me) start the mix in mono and adjust the balance based on that. Then later check it in stereo too. You'll be happily surprised most of the time Another trick is to play the stereo mix and walk into another room, preferrably behind a corner. It effectively sums the mix to mono and you can have a second opinion of the mix balance
This is actually exactly what I've been doing...not really happy with my results (there could be many reasons). I am going to switch to Will's method until I hear or read something credible disproving LCR...I've been reading a lot of articles/blogs last few days and I am so far convinced. But I'm a noob and don't really know much.
Not trying to bash your approach at all, I just thought it was cool that it was the same thing I came up with. When you say "t takes some effort to get the stereo balance correct though.", what seems to affect that? Does it change from amp to amp for you, or from song/song type? I always never had any indication that I was getting it "right", just seemed like I was fumbling in the dark when panning. I did use the 75-90 range though
By stereo image, I mean the tone difference between the two sides. Eg. if you have a very bright and midrangey amp on the left, and then a really thick and dark sounding amp on the right, you need to do some extra work to make the mix more balanced so that one side does not dominate completely. Volume, channel EQ, etc.
I'm more a metal mixer, and there quad tracking reigns supreme for anything beyond demos There are a couple of approaches to quad tracking:
1. Record two times with Amp 1 and pan both tracks eg. L100 and L75 - L90, then record another two times with Amp 2 and pan both eg. R100 and R75 - R90
This will give you a very wide sound, as the two different amps will result in a different enough tone that you can really "feel" the width. It takes some effort to get the stereo balance correct though.
2. Record two times with Amp 1 and pan them L100 and R100, and then record Amp 2 two times and pan it eg. L75 and R75.
This will give you a thicker sound with better balance between left and right. However, the stereo image can be far more narrow-sounding compared to first approach.
3. Record four times with the same amp, and pan eg. L100, L80, R80, R100.
This makes the sound bigger and tighter, but needs some extra effort to get a well-rounded tone, as you cannot rely on Amp 2 to fill in the blanks, so to speak.
Ooh, just missed this 
Well, my Cubase 5 64-bit still works just fine
And as the amp has many tone variations by design, there should be several profiles
Toslink SPDIF. That's what almost all interfaces nowadays use. RCA is a bit old school and requires an active converter.
Optimally, keep the RCA and add the Toslink.
I profiled a couple of cool patches for the famous Boss HM-2... with the specialty being that this is for BASS Probably will not sound nice with a guitar (no amp...).
You'll find them in Rig Exchange:
JU - Boss HM-2/12:00
All settings at 12:00. Kinda gritty and a bit sludgy.
JU - Boss HM-2/Messy
My favourite, really deep and heavy fuzzy explosion for Doom
JU - Boss HM-2/Sludgy
A bit more traditional grit with clearer attack
JU - Boss HM-2/Sunlight
The holy grail. Everything at MAX! Just like the classic Sunlight Studios sound this pedal is most famous for Though for bass guitar, it's not all that impressive unlike for guitar.
Have fun! 
They are now up in Rig Exchange. You can find them by searching for: JU - MXR
There's four of them:
JU - MXR M80/12:00
This has all the settings at 12:00 with effect and distortion enabled. Quite mild.
JU - MXR M80/Crisptort
This one is a nice and crispy distortion for Metal
JU - MXR M80/Gritty
A bit grittier one for Rock
JU - MXR M80/Wizardry
This goes straight into Electric Wizard territory. Heavy fuzzy bass for doom metal and sludge.
Enjoy!
I created some profiles of the MXR and will add them to Rig Exchange today.
