I believe in listening to music in the format it was recorded in. If it's recorded in two channel, as most is, I find it "better" to listen to it in pure two channel with no added effects.
If it's recorded in a multi-channel format, as some dvd's (and SACD, if that's even still around) are, then I use it's native (multi-channel) format.
Depending on how they are mixed would have bearing on the surrounds. If it's just room ambiance, then small surrounds will do fine. If it's mixed to draw attention to the surround channels (Pink Floyd, anyone?) then a bit bigger might help.
Given my druthers, for surrounds I wouldn't necessarily go for floor-standers but if they offer a choice of matching surrounds, I'd not go for the smallest one they offer.
Now, AV receivers offer many opportunities to try to get a semblance of multi-channel sounds from a two channel source and some people love these. You've got a plethora of digital processing options available to play with and see which one, if any, floats your boat.
Personally, my music is always in two channels, aside from the times we have a party and want "music" from all speakers, in which case I'll use an "all channel stereo" mode.