I have very limited experience with it, just played it in a store quiet a while a go, so your mileage may total vary...
anyways, I think the Koch has a very unique voicing, kinda like a marshall, but way darker, and it has a certain growl, that I have not heard from any other amp.the second channel was my favourite, it was tighter than channel 3, it goes from slight crunch to prettey full distortion, but for real metal sounds, I had to max the gain. Channel 3 instantly has more gain, way more than anyone would ever need, it sounds wider and deeper, but it also is not as tight as channel 2, kinda spongy, better suited for lead playing i think. but a tubescreamer in front might help a lot, but I had no chance to try that. I don't remember much about the clean channel, it was more than just useable, but I did not spend much time on it because a clean channel was not my concern when i demoed the amp.