Your M22s will be good enough that you'll quickly get angry with MP3 music. You'll be able to tell the difference. Store your music in wav, flac, or apple lossless (depending on your computer/player).

That's unrelated to your question, but worth mentioning.

For $500 you could find a very good used Nakamichi RE-10 or AV-1s or AV-10 or something along those lines, I bet. It might take a while for one to pop up, but their sound quality is excellent.

Those are old though.

I'm a big fan of scouring Audiogon for great deals. No need to buy a $500 receiver when you can find a $2000 unit that's used a bit. They're broken in for you and sound way way better. This is especially true since you just bought nice accurate speakers, so you'll notice the difference in quality. Since you're not looking for advanced HDMI features or eight million varieties of 9.2 surround, you can pick up a great deal on a slightly older unit from someone who does now need/want that stuff. I bet there are also plenty of Onkyos and Integras out there within your budget.