Several things need to happen for a good profile. Here's what I've learned so far - would love for others to chime in, especially pros like Radley.
1) This is a real no brainer - you need a decent guitar and amp. Sure, really bizarre sounds are sometimes cool, but am I *really* going to play a gig using a profiled Marshall battery amp? Ditto on the guitar - tune up, make sure your intonation is good, etc. I have no idea how much it would make on the refining profile phase, but an in tune guitar is only going to help IMHO.
2) Location. You need a place for the amp to be where you can't hear it when you monitor the Kemper. I have my home studio setup upstairs in one bedroom (control room) and then a game room where I record. But it leaks too much for profiling. Ended up profiling downstairs in the garage with cabling going from the laundry room (empty) to kitchen, where I set up a small mixer. Works MUCH better because I don't hear the original amp coloring the original sound through the kemper when profiling.
3) Recording gear. If you have 2) above set up well, then you can hear what you are profiling and either try different microphones or placement. I wasn't happy with a single SM57 mic, so I bought about $400 worth of recording gear. It made a HUGE difference. Here's what I'm using now:
SM57, Sennheiser 609 silver, MXL144 ribbon mic. The MXL is $100 at guitar center, and adds a lot of depth. I put each mic straight on the speaker, two fingers distance from grill cloth, and about 2cm left of the center of the cone. I also used a flashlight to see the speakers - where I thought they were and where they really were - two different things. I ran these three mics into:
a Yamaha 12 channel mixer that had 4 mic inputs. The ribbon mic had to go into a ART mic tube preamp that supplied +48v. Then the signal from the ART went into the Yamaha. Yamaha was $99 at Guitar Center. Tube preamp was $69. This allowed me to take each mic and hear what it sounded like.
The Ribbon sounds full bodied, but lacks high end. The SM57 and 609 have plenty of high end and add a little pleasing 'grain' to the sound, but not much low end or midrange detail.
I ended up blending all three. The SM57 has a higher peak than the 609, so I dialed in the SM57 first, then added the 609, then blended in the ribbon mic to add low end until it all sounded balanced.
4) Finalizing. This is kinda a voodoo thing IMHO - but this is what I do now. I make sure my guitar is in tune (I usually use my Tom Anderson drop top w/Feiten tuning system) and play several chords in different inversions all over, including diminished and augmented. I try to feed it as huge a palette of chords as possible instead of playing say 'smoke on the water'. The Kemper usually sounds better than the original at this point - I'm noticing the Kemper profile usually has a bit more high end and some less mud/murk in the lower mids. It's still crazy close, but you can hear a slight difference.
Then after I save my profiles, I take them into the exchange and upload, using the upload as a way to 'clean up and enter' info on the profile. I HATE using the dials to put stuff in like location or cab type, etc - would rather wait until I get done and then do em on the exchange.
Comments or suggestions? I redid my Bogner Ecstasy profiles and did a set of Fortin profiles with a Mesa oversize Armor cab. They all should end up on the exchange eventually.