FWIW, I had great success with Phantom Center Channel (until I got a real center). However, I always had the 1050 configured to with no-center at the same time. I cannot imagine what requirement, would prompt you to run in Phantom mode with a center channel speaker present.

This sounds a lot like the problems with Harry Potter on the rear channels, where turning off the rear surround speaker but running in 6.1 mode causes a loss of speaker volume.