Here's the deal..
Everything is a "balance" when it comes to setting up a systme properly. That said, the downsides of full range speakers in the rear, in typical rooms, often overshadows the "up-sides" or pluses! It can be done, but not usually, given the constraints/variables often involved inthe acoustics and setup of the rooms in most homes, from what I find.
It's much easier and practical, to get smaller speakers up higher, for better envelopement, lack of localization, etc, first of all. Second, even if you can get large full range speakers in the rear, placed higher for proper effect (so their not "banging away" in your ear, pulling you out of the movie, and away from the front main soundstage), this often means placing speaker near walls/boundaries in most rooms, which is usually NOT THE BEST SOUNDING place for large full range speakers! And if you can get the large speaker out in the room for bette sound, that often meands placing em on the floor behind/besid you, which is anoying and too close to your ears!!!
Playing full range, place near walls,(as "large") will make for boomy, peaky, unatural sound this way, and you want "flat response" ideally, and smaller speakers are an easier task here. You then would route the bass to a powered sub.
Another consideration, is that active commercial subwoofers are much better addept at handling dynic DD/DTS bass material than passive woofer designs in speakers! The result otherwise is often distortion, bottoming-out of woofers, compressed bass (especially with a receiver driving your speakers), and a less efficient system.
Infact, I often still set large speakers to 80hz crossover, which is actually a more dynamic situation even! Again, letting deep bass go to the sub. That deep info is mostly bass that needs serious power output and efficiency.
All that, and I'm saying, as long as you place rear speakers for flat response, flat coupling down to the crossover, place em high enough above your head for proper soundstage, and route the bass to a well placed, dialed in sub, you'll do well! Otherwise, I think you'll find too many down sides to the "full range rear" setup!
