Two subs or not Two subs?

In a room that size, two subs might be better than one.
Adding bass traps would make a much better improvement if you do add two subs.
I use one sub, but my room is much smaller than yours.
Another idea, try one sub first, and if you feel like it's not ballanced, then get another. With the room being deep at the listoning position, one sub might work fine.
Good luck and keep us posted.

30hz to 120hz is quite good. Stan is probable talking about a used sub that may be discontinued. Look on the classified adds here on AGon.