I have a Univalve. It's the only amp that's made me break my self-imposed "Z's only" rule I instituted about 10 years ago. I bought it without hearing it based on curiosity, a review by Myles, and the knowledge that THD makes real quality stuff. I definitely like it, and here's a few observations:
1) It's built like a tank. It oozes quality. Even the pots feel great.
2) It's loud. That's a matter of physics and also the front end design of the amp. A KT88 is real loud; louder than my Carmen Ghia.
3) A lot of the "brightness" comments come from the fact that at lower volume knob settings, a bright cap across the volume pot comes into play. I run mine at full volume (which nullifies the effect of the bright cap) and use the "Roll" input (I'm also a somewhat cleaner player).
4) Because of the clarity this amp has, tube selection is ultra critical. Use NOS tubes for best results.
5) The preamp tube selection is even more important than the power tube selection. The amp is capable of lots of gain; I use a 12AY7 or 12AU7 in the first position and a 5751 in the driver position quite a bit. It you go with two 12AX7's and use the "Rock" input it gets ultra gainy and mushy.
6) The amp has a real clear treble response, but IMO does not have the "non-fatiguing" highs of a Dr. Z. After a while of playing it at even moderate volumes my ears tell me about it.
7) The preamp design is well engineered, but does not have a lot of "character", since it has to play well with all types of output tubes. Some would definitely call it "sterile"; I kind of see it as "hi-fi" or somewhat "neutral" sounding.
8) A great tube like an RCA Blackplate 6L6, with the lower gain driver tubes, through the "roll" input with the Attitude control on max does a real cool blues sound with a Strat.
Phil