For anyone interested, and also to clear questyles north america's name. I think I figured out why I was hearing the channel imbalance at low volumes but not high volumes. Really stupid really. The new amp is from a different product run and the volume knobs do not line up completely. So what I thought was 1/4 way on the knob was actually less than that on the new amp vs the old one. Which explains why I heard the imbalance at low volumes, but as I turned it up, the imbalance went away. DUH.
For those with dual monos, I added a tripp lite UPS the other day and it seems to have made a very positive impact. Especially noticeable to me when running my modded HE-6's (grill, fuzzor, vegan pads). First time I listened to them with the UPS added, I immediately noticed that soundstage was very holographic, 3D. Bass also seemed improved. I brought the UPS because I thought my system seemed to sound slightly better at night but its made a significant difference. As always YMMV, etc.