A small REL, and not a pair, will be enough. If you need to locate it away from your other components, get the Arrow wireless connection. T5x or Tzero Mk III should be enough. Alterntively, the KEF Kube 8 MIE or KC62 might work. The KC62 would be the most expensive of the lot.
Small footprint subwoofer
I am in the process in replacing my current sub for a smaller one. I dont want overwhelming bass that will effect the music. Just articulate, musical bass that will be easy to integrate seamlessly. At the moment, I am about to get a REL R218 to replace a Hsu STF-2. Keep in mind this is in a very small room(10x10x8) so for the reason of getting a small sub. If all goes well, I might consider getting another REL with the same model if available and go stereo pair. What are your thoughts?