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.
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.