jb 1309,
1 - M60/M50.
Generally it is said that the M60's, as mentioned by the previous poster, have a clearer midrange and will bring out vocals a bit better as it has the midrange driver. The M50's are closer to the M3's and M50's in sound - a more laid back sound. By laid back, we mean the midrange is slightly less loud, so it sounds recessed in a sense. I own the M3's and M80's (which are almost identical to the M60's in sound) and prefer the M80's, but both sound amazing.
If budget is a concern, and you are going to use these speakers mostly for HT, then personally I would get the M50's (or 40's if it was even more of a concern). If you want the clearer sound of the M60's, try the M22's and combine them with a sub. I used to have that setup and it's very sweet. The M22's are extremely transparent speakers.
2 - QS4's
yes, they will match nicely. They will just put out slightly less sound. In a room your size, however, they will fill them nicely.
That being said, the QS8's will, of course, envelop you in sound and spread the sound out more. It's a matter really of budget at this point since the QS4's now use the same tweeters as the QS8's, and thus the same in the entire Axiom line. Axiom used to put a tweeter with a smaller voice coil in their lower priced models.
