Just to add my 2 cents...I recently purchased M80's. I'm adding an amp because my AVR didn't satisfy me with 4 ohm loads (aka M80's and the VP180). However, many here that have no problems with an AVR running M80's but that has not been my experience, YMMV!
Adding an amp can be an expensive option and you've said your budget is limited. The M60's, and the rest are 8 ohms which are easier to drive with an AVR...Hell, now that I think of it just get an amp! When you get more tax money upgrade to the 80's, Problem solved!
Seriously, since you can't do the center...I had the 150 and while it's very good the 180 is just better period...and you want better bass then the EP500 may do it! The 80's, while great, won't do anything that your sub isn't doing already.
Personally I'd upgrade the QS4's to the 8's and yes, there is a difference!
