I noticed a similar effect when my amps were plugged into a Quintet. There was a muted/compressed quality to the sound that didn't exist when plugged directly into the wall. From what I understand, all amps have built-in power filters. The better the amp, the better the filter. If you like what you hear when plugged directly into the wall, why not do it?
FWIW, I hear an improvement with my preamp and source components plugged into the Quintet. That's how I use it.
FWIW, I hear an improvement with my preamp and source components plugged into the Quintet. That's how I use it.