I am convinced your power conditioner was ruining your sound too. Brown power with voltage drops is not the same as "dirty" power resulting from digital and/or high frequency noise, and does not have the same affect on audio performance. Presumably your APC is dealing with the brown power problems?
I have yet to hear a power conditioner that improved the performance of an even reasonably noise-free AC supply from the wall. PC's definitely make systems I have heard, including my home systems, sound "different", often "smoother" but not better if the AC is already fairly "clean" IMO. Dynamic peaks get clipped and smoothed over, so everything starts to sound like Steely Dan's early to mid-seventies mega-overdubbed mush.
This doesn't mean that there aren't conditioners out there that can significantly improve system performance by scrubbing noise from the wall supply in difficult AC environments, or reduce pollution from your digital gear back into the AC lines - I use a power conditioner with my sound system in my office in a highly polluted office building electrical environment, but this is the only place I have found a benefit to date. In agreement with Mingles, I am especially dubious of putting something in the line between the wall and your amp - in fact I am temped to hard-wire my amp at home directly to the AC supply line in the wall!
If you need multiple outlets, try this piece of gear instead of a power conditioner in a reasonable AC environment, plugging your amp into the first outlet or directly to the APC, and your digital components into the last outlets used -
http://generubinaudio.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=GRAS&Product_Code=Wmold&Category_Code=acc
Finally, I wonder if you tried unplugging your APC from the wall and running your system off the battery alone for a few minutes. That might provide the best sound you can get, albeit for short listening periods!
