My home theater system is anchored around an HT1/HTS and HTC speaker setup (the four surround speakers are in-ceiling Triads). Jim and I co-created what he now calls the HTS subwoofer. I originally started out with only the HT1, thinking that I would later add a single, separate subwoofer. I later decided that I also wanted a good-full-range system for 2-channel listening and drew up plans for Jim for a sealed subwoofer using a 12" TC Sounds driver. The advantage of this approach is that I get great, bass effects for HT (my room is 20x22x9) as well as tight, 2-channel bass for more critical listening. The HTS module serves as a stand for the HT1. I use an external electronic crossover that both splits the highs and lows to the HT1s and HTS, respectively. This same crossover has an LFE input (from my HT receiver) that I can add into the 2 bass channels. I amplify the HTS subs with a Crown K-1 amplifier and equalize same with a Behringer DEQ2496. Overall, I am very very happy with this arrangement. I think I get HT3 or better performance this way, with the added advantage of bass mode equalization and a ton of power from the Crown amp.
I would not be concerned about your room being too small. Physically, the HT1/HTS combination has a fairly small footprint. And the minimum space required behind the vented HT1s is less of a concern because the equalizer rolls off (for my system) at 100Hz. The ports in vented system are most active in the lower octaves so backing them closer to the wall isn't a problem because their output is highly rolled off (I use an 36dB/octave slope in my crossover). This, of course, ignores any consideration of speaker placement driven by room modes...
I would be happy to post a picture of the HT1/HTS speaker combination but, alas, I cannot for the life of me figure out how to upload a damn photo.