Richard Gray is a Parallel Current device not a power conditioner. The Monster AVS 2000 is a voltage regulator designed to keep voltage at 120volts.
With a M520 by eastern electronics the music became lifeless with the AVS2000, this device worked best with my home theater and the big screen TV. With my 2-channel system I really like the Richard Gray, it seems livelier or more musical.
With tubes you already have a transformer to change the voltage of the line, I think the interaction with the transformer in the Monster AVS 2000 and the transformer in the tube amp changed the sound for the worst. Solid state equipment also have transformers so most sites recommend plugging your AMP into the LINE not the power conditioner. Use the power conditioner for the TV and the misc devices. However, I use a AVS 2000 in my home theater and plug my Amp into it also, I donÂt think the AVS 2000 changed the sound with this piece of equipment.