As for using the three π as a sub, sure, you could do it. It provides nice full rich bass that doesn't draw attention to itself. But it is really designed for use as a full range speaker, and you can get deeper bass from a design tuned for use specifically as a subwoofer. One example is a LAB12 woofer in a 4.5ft3 cabinet tuned to 22Hz. I can send plans if you're interested.