Your Denon will be fine.
You don't mention your intended use (movies v. music, size of room, etc.). I'm guessing that - since you are getting an IW/OW center, you are looking at a pretty clean install for viewing content on a flat screen.
If you have the M80's, you probably don't really need a sub for music or for most TV. If you are watching movies, you're going to want quite a bit more sub than an EP175. If you have room for M80's, your room is probably too big for an EP175 to be effective.
IMO, M80's are overkill unless you have a pretty big room AND you will be playing content at a pretty high volume. I mean, "I just want them" is a totally valid reason, too, of course. But if you're going to be watching movies and have to balance the budget, I'd get more subwoofer and less main.
Check out the wire table and other information at Roger Russell's site
. 20g wire might be okay up to about 20 feet IF your speakers are also a pretty easy load, which the M80's are not.