Was your brother-in-law's sub new or used?
I use my Hsu VTF 3 in a 2400 (roughly) cubic foot space and it pressurizes the room just fine for me. The gain knob is not even past the first little hash mark, about 2/3 of the way there. I put the sub in the corner farthest from all other openings (kitchen and hallway).
I haven't tried testing the limits on the sub, so I don't know what it takes to get it to bottom out or chuff. "War of the Worlds" is definately the movie to test the limits with.
Is the HT area closed off from the rest of the basement, or is the sub trying to pressurize all 7200-8000 cubic feet? That's a lot of space.
I don't have much experience with large spaces and HT, all my travails have been with cramming everything into really small rooms.
I think craigsub can probably give you the best estimate of the Hsu's ability in a large room.
