im gonna get 6.5 inch reference premium series for the back, but im not sure which i should get, is there that big of a difference in sq?

Coaxials are more than enough. A lot of audiophiles (pun?) have NO rear speakers while others say rear fill (faded to a low level) is needed for a fuller sound stage. I've never heard of anybody putting components in the rear so that should say something.

And Joe has one hell of an amp (Macintosh 6ch) and there's no reason to waste that on poor quality speakers.

But yes, I do agree that you want most of your soundstage up front.

I remember some people will put a single or a pair of 6" or so midbass component speakers in the rear in order to fill out the sound stage. There are so many variations, keeping a stock look, etc., but obviously some will sound better than others...