If I'm not mistaken, the Macintosh is an analog multich channel preamp, right? If so, you can forget dynamics for movies. You're then relying on the processing in your dvd player and other sources, and your not getting the gain you need for proper dynamics and such..my experiences anyway...and that's a lot.
I could be wrong on the Macintosh, but I don't think so.
What speakers are you using anway? Makes a differnce.
Yes, receivers ARE NOT as good sounding as good separates, and usually not as strong overall, depending. In short, you'll have some compromises often.
Still, what has been recommended above, and what you're considering are, yes, the better receivers. Older 5.1's that sounded pretty good are Arcam's, Sony 777es, Nak AV10, Marantz SR14/18/etc, Denon 4802/5803/yada yada, Yamaha RXV1/DSPA1 and such.
Still, I find no "super receiver" that's going to replace good separates anytime soon. But you can do bass mananagement on these to help your power and dynamics, and at least get descent sound with the right piece, yes.
Might consdier the sunfire piece...heard it once and it did sound promising overall.