Down firing sub

I am setting up a HT and 2-channel system in our new house. The room is circular and the only plave I can put a sub is in a built in alcove in the wall by the TV. My wife will not allow it in the room and there is no way to run the wires. I can make the built in "niche" as large as I need it. I am looking for a sub that will give me good HT and 2-channnel music. I assume I need a front firing sub. What would be best? The Velodyne is front firing but the REL is downfiring. What do I need to do to the enclosure to isolate it. Anyone with experience with this? Your help is greatly appreciated.

TB