It's a preference -- no more, no less.
Amen brother, Amen.
I prefer 2.1 stereo for most music. The only times that I prefer 5.1 is when the recording itself is actually presented in Dolby Digital 5.1 or DTS. Things like concert DVD's or SACD's specifically mastered with 5.1. Those 'work' for me, as I usually feel that the recording does feel more real, with ambient sounds around you, proper reverberations and echoes of the venue, etc.
Perhaps it's the result of a 7 year old receiver, but DPLIIx:Music and DTS:Neo Music modes don't do anything for me. They always sound overprocessed and just sort of 'simulated' to me. In other words, I find that the effects detract from the realism of the recording rather than adding to it.
Movies are an entirely different beast. For movies, I always watch in multi-channel modes. Even old stereo movies I run through DPLIIx:Movie. IMHO, that does work pretty well at creating surround-sound effects from 2.0 sources. Nowhere near as convincing as true 5.1+ digital tracks, but better than just stereo.
