I just tried it and I cannot hear a single difference between Stereo and 7.1 modes with 3D off. This was tested with music and with stereo pink noise. Are you certain you have the room emulation working with 3D off in 7.1 mode? Are you on a beta firmware or the public v3 release? When I was on v3 I don't remember 3D off being any different from what it is now. If you are on a beta v3 firmware that could explain it. They had a "3D On" mode (no headtracking) while the public one did not due to stability issues. It could be that your "3D Off" got switched with the "3D On" mode and that's what you're hearing.