System update
The Luxman is gone. The McIntosh C2700/MC 611s sound glorious with the KEFs. The bass is easily 300% better. I could probably convince some that I am using a sub.
The moral of this story is that room acoustics had nothing to do with the bass. It was the inability of the Luxman to drive the power-hungry KEFs. This fact was verified at a dealer also. I also tried the 509X at the dealer into the KEFs, there was a slight improvement, but neither of the integrateds had enough juice to drive them properly. Only the M10X could. The dealer also agreed.