Read Morgan Audio's thread about the RSL Speedwoofer 10S. I think the three subs mentioned there are your real competitors.
If you want a sub for both HT and music, are willing to swap the tuning set-ups when going between the two, and don't mind a pretty large sub, the Hsu is probably your best bet.
If size is an issue, the Emotiva may not be a bad compromise if you are just as worried about HT as music.
I am primarily a music guy, so if size didn't matter, I think the Hsu in sealed mode is probably the best bet. I am lazy enough be content not having the deepest bass for HT, so I would generally leave it in the sealed configuration. However, it is a plus that I could reconfigure it for deep HT bass for a "special event" or special movie.
As a music guy, and, if size did matter, I would go with the RSL Speedwoofer.
For your room size calculation, you need to include the volume of the apace beyond the "open wall" which make it sound like you have a pretty large volume. Reality check - $400 won't get you a pressurized room, but in a similar situation, I have been pretty happy with "inadequate" subs as long as I'm not trying to play at reference levels.
