Fretburner,
I have to support Skunkyfunk on this... the EL34s in the rivera tbr1 really sound more fender than a lot of fenders on the clean channel. Despite the fact that the Diezel Herbert has a circuit that is not really a copy of the classic circuits we know. It for some reason can sound very similar to fender and marshall but not exact because it adds its own Diezel mid which really sounds nice. In the end, it really boils down to channel voicing. The Rivera TBR1SL was the first amp that proved to me that you can get more fender than fender on EL34s.
If there is one thing the Herbert Diezel has proven, it can do things outside of the well accepted norms and conditions we have gotten used to amps. I even dare to say that this is true amp modeling because of the variety of tones and tweaks available. I dont mean it to be amp modeling in a POD or Line 6 way which is really preset timbres but rather dynamics with variable sonic palettes at your fingertips.
On channel 3 gain, I am happy with the amount of gain. We did not get to try a high output humbucker. If we did, I am sure that Skunky Funk would have found the gain sufficient. On the other hand, the uberschall really has more gain but then i really dont know if you would have use for more gain. I seldom get past 12 o clock on the Uberschall and it takes a really special guitar to handle the gain past 12 o clock.