Whether a Hsu sub or anybody else's manufactured sub, it's well discussed the benefit of having two subs and having two subs has everything to do with quality of sound.
One wants to have a minimum of two subs so as to smooth out the bass nulls in a room that are naturally cause by conflicting reflected sound waves running into each other and cancelling each other out in the process.
I am not sure whether your room size is the one driving it (or) the space to fit in the sub that is making you say "it may be too large". Can you please explain ?
My apologies for not being crystal clear...it's more of a space problem than anything. I'm also not sure with the carpeted concrete floor if I should go with a down firing or front firing sub. I'll mostly be using if for 80% movies/TV and 20% music.