Hmmm... I went back through this thread rather quickly this morning, and it sounds like the most likely source of the problem is the Rotel 991 amp. The impression that I get is that previously you were able to calibrate all channels with the master volume set at 0dB and have perhaps 7dB of variation between channels (with the mains perhaps being dialed higher than the other channels due to a lower efficiency). It also sounds like moving one of the mains to the other amp (the 985 MkII) largely alleviates the problem. That makes me suspicious of the 991. Have you got a local Rotel dealer who can do some troubleshooting on it? Barring that, can you put the center on the 991 and see what happens to the test tone through it?