Others will chime in that are more knowledgeable, but I personally can tell from my experience that right now I am needing a dedicated amplifier because I didn't think I would need one/was too cheap to get one for my new system of M60s/VP150/QS8s a few years ago at the time. If you're in a large room and like to even occasionally crank up the volume you're much better off getting a dedicated amplifier. I'm regretting not having one now because the sound gets really harsh with the amount of power my current AVR supplies, and am shopping for the best option right now.
I'll have to replace my current AVR as a result because of the lack of options it has for a truly powerful set of speakers like the Axioms such as ones in the Epic 80 set (such as pre-outs for additional subs and amp). Pay now for decent power or pay later and maybe have to replace whatever AVR you get in the future due to lack of power. You can still get a good receiver at first but really think about external amplifier options.
