If I understand, you have a two channel setup, correct?
If so and you have no desire for more than two channels then no, you're not missing anything.
If, however, you wish to avail yourself of the newer technologies with 5 (and more) channels and a separate low frequency effects channel then yes, you're missing a lot.
FWIW, I'm more than happy wit ha 5.1 setup. My room can't really accomodate and do justive to an additional surround speaker. 5.1 is really quite satisfying though.