Are the amps new? If so, I would either try another amplifier or let the JC's warm up for a few days and see if there's a difference. The JC's takes a while to settle in. If it's not the amps, it may range from something trivial like out of phase wiring to a bad tube. You also can't rule out improper application of acoustic treatments.
But I think Kal is closest - room response from speaker placement vis-a-vis listening position. Try a Radio Shack SPL meter with something like the Stereophile Test CD on your setup. Take one reading from the listening position and one reading a foot away from each speaker. If there's a marked difference, it would point to room response.
Dedicated circuits are not going to cure what you describe. Long cables may become a problem if the amp has a too low damping factor (which the JC don't). A call to Vanderstein wouldn't be a bad idea, either, if all else fails.
But I think Kal is closest - room response from speaker placement vis-a-vis listening position. Try a Radio Shack SPL meter with something like the Stereophile Test CD on your setup. Take one reading from the listening position and one reading a foot away from each speaker. If there's a marked difference, it would point to room response.
Dedicated circuits are not going to cure what you describe. Long cables may become a problem if the amp has a too low damping factor (which the JC don't). A call to Vanderstein wouldn't be a bad idea, either, if all else fails.