I had used subs with my RM30C. I used a pair of ACI Force XL, which were good, but later went to a James EMB1000, which is superb for a very small box. I live in a condo, so I'm space challenged, or I would have used the VMPS subs, which are truly outstanding. Of the many small subs I've owned, only the James is close in quality, but not quantity, to the old VMPS larger sub, of which I've owned 2 pairs.