Regardless of the brand of your equipment, having multiple subs provides a number of benefits. In addition to the article already mentioned above, the pioneering work in this area was done by Harman International as revealed in this white paper presentation:

http://www.harman.com/wp/pdf/multsubs.pdf

I found this immensely helpful and benefitted greatly from following the overall process.

Good luck as you look for the perfect bottom end! (Keep it clean.)