need recommendations for sub for music

Hi Everyone,
I recently completed my HT set up with a Sunfire HRS. I love it for its power, tight and clean bass and compact size. But I thought I'd get another small used Sunfire (the Junior, for example) to complete my 2-channel mostly music set up in the family room. It has to be small and cannot be placed in a corner, unfortunately.
But I also wonder what other subs are out there to best complement my system. The family room connects to other rooms in a very open floor plan. I have the Denon AVR2808ci receiver and a pair of Paradigm Studio 60s. The set up is mostly for music.
I have a small budget, so I am looking for a used sub on this site.

Thanks for your suggestions