A lot depends on how the program/movie was mixed in post as some mixing for surround is better than others. Sometimes, the kind of audio the original had will affect how you hear audio. In other words, some original movies were in mono, so the post production company sometimes does a little trickery to attempt a 5.1 mix. Or, nothing is done. Some are stereo sources, so you essentially end up with the equivalent to Pro Logic instead of a true 5.1.

As far as all of the versions of surround, my understanding is that 5.1 uses two rear corner speakers, 6.1 adds and extra rear speaker (centered between the two rear corner speakers), and 7.1 adds two additional speakers, one for each side-wall between the front corner speaker and the rear corner speaker. The 7.1 in theory, replicates how some of the higher-end theaters have their speakers set up.