I recommend finding a very small powered sub from a reputable brand (REL or Velodyne MiniVee, maybe?) to fill in the very lowest stuff (no need to run the sub loud), and I second the earlier recommendation to find a way to work a pair of small speaker stands into your living space. Having the speakers on the credenza looks nice but if the speakers aren't designed to take the extra room loading into account then your voices and acoustic bass could sound unnaturally thick.
To find the best subwoofer placement, place the sub in your listening position and walk around the room until you hear the best bass. Once you find the best bass, put the sub in that location, and that's the kind of bass you'll hear at your listening position, because in most cases room acoustics can work in reverse.
