I'm in a similar position.
I have a pair of M80s, VP150 Center, 2 QS8s side surrounds and an EP500 sub woofer.
I want to upgrade my 10 year old Yamaha receiver, and I've been looking at the Denon AVR4810CI. The problem with this is that it's not rated for 4 ohms so it's not going to power the M80s.
I was going to buy separate power amps at a later stage, but now I may be forced to act earlier due to the 4 ohm thing, then I'm looking at the following options
1. Emotiva XPA - 3 (Three channel rated at 300 Watts into 4 ohms) and then I'd run the fronts and center off this for a consistent front soundstage.
I read somewhere that there may be issues with the Emotivas and the M80s. I'm not sure if that's because the 300 Watts isn't enough hence:
2. Emotiva XPA - 2 (Two Channel rated at 500 watts into 4 ohms) and I'd just run the M80s with this.
Both of these options are much cheaper than anything else I've seen, but I'm slightly afraid of 2nd hand comments I've seen regarding people having problems