Looking for a subwoofer to match my GMA Europas

I would like to add a subwoofer to my system to add a little more bottom end to my music. I currently have two Green Mountain Audio Europas hooked in to a Conrad Johnson CAV-50 and have been very pleased for several years.

My listening room is small, roughly 14 ft by 12 ft. My music tastes run mostly to jazz and classical, with an occasional rock tune mixed in.

Any suggestions for a compatible subwoofer would be appreciated. I suspect I need one with RCA speaker connects given my amp, but am not sure.

Thanks,

Chris