I can't necessarily agree with Thesoundhouse claiming your 501's are speaker dependent. I have a pair and have owned Thiel 3.6 and Eggleston Andra II's and the bass has been plentiful and balanced. I have heard them in Brick and Mortar salons with other speakers also. Be careful and check that out yourself.
Good advice above though, spend time with speaker placement, wall reinforcement, and finding bass nodes.
Good advice above though, spend time with speaker placement, wall reinforcement, and finding bass nodes.