subwoofers for spendor A5

I need recommendations for a pair of subs to go with my Spendor A5's. I am using an Audio Research ASi integrated in a 14x 22 ft room.
I have s5es, the precursor to the A5. I use a Velodyne subwoofer with them that works very well - the equivalent current model is the Optimum 8. It provides support for the low bass without overwhelming the speakers. The built in room optimization, flexible input options, and adjustable crossover are all helpful.
REL work well with my Spendors.