First off, a subwoofer is only important for frequencies lower than a full range speaker can handle (which would include basically ANY movie with an explosion). You don't NEED a subwoofer. If you want to hear anything below around 40hz, you should get one. For most music, you don't need it, and it's more important to get one that is tight and not "muddy" if your focus is music. I watch too many movies to live without a sub, but that doesn't mean you wouldn't enjoy a 5 or 6 speaker setup without one.
But you did say your room is small, which makes me wonder how and why you want 6 speakers. The only reason you would go to 7 speakers instead of 5 is to get a more distinct rear channel. In a small room, you can't hear a distinct rear, so there is usually no reason to add the sixth or seventh speakers. Position your surround speakers well, and leave off the extras.
Also, remember you can always de-emphasize the sub, or set the crossover very low. With no sub at all, you will not hear anything in the very low range. You can set the sub to only play at very low frequencies and leave anything above, say 35hz to the speakers. That would eliminate any "pounding bass"