>>Must have been wishful thinking, the mains are M50's.

No problem. I understand the M50s are pretty good in the bass department as well. Good luck with the experimentation.

The answer is definitely to get a bigger sub but with luck you can postpone it until you are ready to get that big honkin' sub you really want

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8