The Theater three π loudspeaker is a two-way design, not a subwoofer. I suppose it could be used as a sub, if the crossover were omitted. It provides response down to 30Hz, and has a nice response curve. But it was designed for use as a full-range loudspeaker.

If I were to recommend a physically small inexpensive subwoofer to match it with, I would suggest a LAB12 in a 3.5ft3 cabinet tuned to 22Hz. Crossover to the three π between 60Hz and 100Hz.