Wow great feedback! Thanks people!
Go into your Denon's settings and set your front speakers (M3's) to large and in the subwoofer settings in the receiver change the subwoofer to LFE+Mains and a 80hz crossover for all speakers. Then play a movie and some music and listen for any differences and what you think about it.
I tried this last night and it sounds better than it used to. I'll leave it like that for a little while before I make up my mind but sounds like a good direction.
Also have to try grunt's suggestion of raising the crossover to see if the issue is really with the M3s.
I also mentionned to my GF that getting a bigger rug could help... should've stayed mum on this she's already shopping!
