I disagree with these posts.
Had the rackmount vtwin/pa power amp back in the day(~2002), i remember it sounded awesome but the power amp was so heavy i ended up selling it.
Then used a 1973 Orange OR120 for a long while, and used a vtwin pedal to dump mids and clean up the tone. (Worked less well as a distortion pedal.)
Cut to 2019, and the world of That Pedal Show got me interested into pedalboards and effects loops. I remembered how much I enjoyed the vtwin as a preamp so tracked down a 20/20 Dynawatt and ran the vtwin pedal into this. The clean channel sounded phenomenal, but the overdriven channels sounded kindve muddy. I remembered the rackmount version had an fx loop, so tracked one down. I had forgotten that the FX loop has a STEREO return. So if you run only one return to the preamp and both outputs from preamp into each of dynawatt's channels and speakers respectively, and INSTAnT Wet Dry , and sound is crisp and clear in all modes!
Granted I am running some primo pedals in the fx loop (most importantly a maiden D), but running all the same gear, I honestly have a hard time playing any other amp setup!
These were ahead of their time, and a comparative steal when you compare their current price and extensive feature set!