subwoofer recommendation

I have this secondary system that I use for multiple rooms. It is my older Dynaco pre-amp (van alstine mod), Hafler 200 (Musical cooncepts mod), an Adcom speaker switch box, and a couple of pairs of EPOS els3's. So, I want to put some low end into it, but the speakers are up high over kitchen cabinets in one case and a huge fireplace mantle in the second. So, what type of smallish sub can I use that sounds half way decent and can be placed up high?