>>My issue is that H/K doesn't have a spec for driving it at 6 Ohms nor do they suggest that you should drive it at anything less than 8 Ohms...
You are correct about the specs, but the funny thing is that the most common recommendation for driving M80 (4 ohm) speakers is either an HK or a Denon. The HK really is much more capable than the specs would imply.
Anyways, like everyone else is saying any receiver in that range is going to do a great job. Just keep in mind that for 4 ohm loads Denon and HK tend to be recommended over Yamaha (admittedly based on anecdotal evidence).
As far as I know they're all fine with 6 ohms. I guess I would probably cast another vote for a Denon 2805, at least that's what I would get if I couldn't get my HK again.
Anyways, try 'em all out, poke at all the remotes, see which one you think looks best. They're all really good. Unfortunately the specs are all written to somewhat different standards so a spec-based comparison isn't going to do much for you. A feature-based comparison is still OK as long as you focus on the features you want. Denon (and probably Yamaha) have more options for A/B surround speakers, for example. HK on the other hand has their Logic7 matrix mode for stereo content which is still my favorite way to listen to 2 channel CDs.
Denon and Yamaha have a more elegant look -- HK is very modern with a cool blue LED in the volume control. What the heck, it all matters
