It is odd! I do have the Outlaw 990 but I don't have any attenuation set for stereo, 2-channel music. The setting is at 0dB and doesn't cut the subwoofer. However, it's possible that the signal sent to my sub in 2-channel stereo is too weak and that the signal in DBIIx Music is correct? But it definitely sounds a bit boomy when I switch to DBIIx Music.
I have to admit that I haven't played much music yet via DBIIx Music. For now, all I've really played is some country (i.e. Dixie Chicks) and some light rock (i.e. Dire Straits, Clapton, Blue Rodeo). I widened the front stage by setting the Center Width to 5. Previously, it was set at 2 and it seemed to compress the front and route everything to the center channel, which I did not prefer. Setting it to 5 seemed to widen the front stage without diffusing the vocal. Setting it to 6, however, did diffuse the vocals too much and spread them out to wide. I also set Panorama on which also seemed to widen the soundstage but didn't diffuse the vocals.
Admittedly though, I'm not really an audiophile so my ear can't be trusted too much
But it does seem to sound pretty good too me - so far.