Tough to make a recommendation when neither party has heard the speaker set, but James Larson is a pretty respected reviewer and that's a very positive review linked to above. You already have the subs covered so the Monolith should make for a fine setup. With the upstairs having a railing it would have behaved like a larger space. If the basement room is around the same 14x14 but with a door then you should be fine for power and speakers. You'll want to pay attention to good speaker placement and with two subs the usual recommendation is along the middle of a wall if possible or in the corners, but that's often something you have to experiment with to match the room. Some assistance available here once you have everything in hand.