1 sub? 2 subs?

I'm interested in adding a sub(s) to my current system. My system is used for both music (75% of the time)and HT. In adding a subwoofer, I would like it to be as musical as possible...explosions etc for theater are less important since I think of those types of sound as more for entertainment vs. something that must sound exactly right (anyway, I have no idea what most of the explosions really sound like because I've never heard it in person). My front speakers are Sonus Faber Concertos. The room is 16x25 with 9 foot ceilings and opens up into another room that is just as big.

I've been following many of the threads here on Audiogon(which have been incredibly informative) and have noticed that some feel that 2 subwoofers are needed to obtain the best overall sound. I'd like some views on the issue of one vs two subs in this setup. If I go with two subs could I get smaller subs eg 2 Sunfire Trues instead of one large eg. 1 REL Storm. Also, any recommendations are welcome. I'd like to keep it under $2K and am willing to buy used. Thanks for all your help.
Dave