floorstanders on carpet over concrete

You might try a set of Aurios Pros under the speaker spikes, four to a speaker. They will certainly isolate the speakers from the concrete floor, and clean up the bass. Not inexpensive, but what tweak is these days? Audionuts is one dealer which carries them.

I don't use any Power Line conditioning now, only a dedicated lines. Yesterday I tried to switch to my "old" lines, following the Tireguy's advise- didn't make any difference bass-wise.

Try moving the speakers away from the back wall three inches at a time until the bass firms up. You may end up with them to far into the room so bass traps will be needed. When I ran my dedicated lines the most improvement was bass then detail. As stated above by moving breaker to other side can only effect eq. if the other appliance is running at the same time unless its a frig or something that is on all the time. The most important time to have breaker on same side is when multi dedicated lines are used, you want them on the same phase or leg of the sub panel. In my HT set up I run Paradigms and I find bass to be some what muddy, not as fast as I would like so that's where the sub comes into. I find these speakers need alot of room behind them. I think your best solution will be the bass traps! Another thing get rid of the crappy spikes that came with your speakers and pick some Michael Green Audio Points up as they worked for me. Good Luck Go to my system and scroll down to see my dedicated line project.

Try adding some more cushy furniture in the room. It's free and worth a try if you can move something down there easily.