The effect that I have noticed from power conditioning would fall in the domain of greater transparency (less hash to the sound), but I doubt that power conditioning will make a big difference to the issue that you initially describe.
If you have ruled out room treatments and speaker placement, then I suggest that the biggest bang for your buck in making a real difference in the smoothness of your system will be the following:
1) source - MLs show every flaw in digital playback in big, bold writing.
2) preamp - when I replaced an old NAIM preamp for my current Copland, I was astounded at the way that highs were being mangled by my preamp. At best, a new amp will only highlight issues around a crappy pre, and at worst, a crappy pre will make you buy a sub-optimal amp that compensates (not that your current pre is crappy, but it might be the biggest contributor to your issue).
3) amp - when you know what preamp and speakers you want, it is much easier to get the amp that works best with them.
4) Cables. Touchy subject around here, so I leave no other comment
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To me, it would be a tossup between the source or the preamp as the guilty party. Find a dealer that will loan you equipment, and do some sleuthing - what could be more fun than that?