I use the SPDIF for reamping and i am totally happy with that. But i agree that many users would want to use the USB function for reamping. The problem however is, that as soon as you make the KPA an audio interface, you will receive other problems. Your monitoring routing of your DAW will screw up in most cases, since from my experience, you cannot simpy use one USB Device for Recording, an another one for monitoring. So you would need to use the KPA for monitoring all signals of your DAW.
I would prefer to use the Ethernet Port of the KPA to make some low latency connection (not TCP/IP) over a dedicated NIC in your DAW. By using a specialized Layer2 audio protocol like in those AVIOM monitoring systems you could get audio signals to the KPA without any noticable latency and without changing your DAW audio setup. Just let your DAW communicate with the KPA over a plugin when needed.
Can you talk a little more about your workflow for reamping using the SPDIF? I am trying to visualize the whole process in my head (don't have a KPA yet, US guy). what is everything cabled, routed, monitor out settings, etc...?
I need to make sure I buy the right audio interface that includes the right connections to be able to reamp with the least amount of recabiling required. Someone mentioned using the "montor out" for the DRY signal, but I thought the monitor out is what you would use if you were connecting to a traditional power amp + cab. So wouldn't that actually be profiled AMP minus profiled CAB (and what about post FX)?
With reamping you want to be able to monitor (and possibly even record on another track(s) the full signal path while ALSO recording completely dry guitar.