Thanks very much for the reply. I realize I have likely offended some sensibilities since most folks here are more interested in the dynamics rather than the finish of the product.
For me, I'm just looking for a reasonably priced sub build (5-600) that I can build out of quarter-sawn oak plywood. Form factor isn't a huge concern, but I imagine a build around a 15" speaker might give me the air-movement I need for reasonable response.
I agree, multiple subs for a room this size is the best option. However, this isn't our main viewing area and we'd prefer to keep the system to 5.1