When you set up your AVR you tell it "sub-no", and "front-large". After that all LFE information will be routed to your front speakers (or all speakers setup as large). Remember, if your speakers aren't capable of 20hz output at the least you WILL be missing some LFE performance, since many movies have 20 hz or lower content in them which your speakers will not be able to handle.
Edit: I looked up the Monitor 9s, they only go to 39hz at best. While thats fine for music, you won't get the full LFE slam with movies. As long as you're OK with that your new speakers should be fine.