I recalibrated the system as soon as I put the new amps in. I have 3 different pro audio amps, all with signal meters that all do the same thing. From weakest to strongest: ART SLA-1, Peavey CS-1200H and Crown Macro-Tech MA5000VZ.
Cables are XLR 25 foot balanced cables I use in my pro audio rig.
I almost wonder if one of the pins on the XLR is not outputting a signal.
I should mention using PA speakers with horns and high sensitivity, the low level thermal noise when putting head to speakers is louder on the LEFT speaker then the RIGHT speaker. If one of the left speaker's XLR pins was not working, this would not only explain the loss of 6 dB, but also the increase in noise since it no longer has a true balanced signal.
If this is so, my posting should be worded "left channel quieter then right". I'll have to do more testing...
BTW here is a before and after picture of the setup:
Before:
After:
Rears: