Without having heard your system, which seems very good, I'd say first check for correct polarity to speakers (+ to + and - to - for each). If not connected properly, bass is affected.
Also confirm that your speaks are well positioned for good bass in your room.
If these check out OK, then add a good sub or two, as was suggested.
Also confirm that your speaks are well positioned for good bass in your room.
If these check out OK, then add a good sub or two, as was suggested.