Guys,
Thanks for the input; I unfortunately was already told by Polk's support that the RTi12's, while adequately demanding, won't be a problem to drive with my setup depending on the demands I make of it...this is what they said:
The RTi12’s do look imposing with their high power handling capability and multiple drivers, however they are not a particularly difficult load to drive. They are not low impedance, nor low efficiency- which are both factors which make a speaker difficult to drive or “power hungry”.
I was also told by someone on Polk's forums that the 12's will be fine to be driven by the 605 -- I'll supply those replies here in a moment...
UPDATE: Here's what I'm being told from Polk forum folks...
You will be fine. Could the 12's use a little more power, yes they could, are they going to be just fine with the 605, yes they will. Get them all set up, listen to them and then down the road if you want, get a better AVR and an external amp and call it good.
and...
Your 605 will do just fine
and...
Take those power ratings with a grain of salt. The 12's are rated for a "max" of 500 watts IIRC. You could take a 500 watt amp and hook it up to a pair of RTiA5's though, with absolutely no drawbacks at all. There is no such thing as being able to "handle all that juice", when it comes to loudspeakers.
and...
You're going to be absolutely fine powering the 12's with your AVR. Bass is what creates the most demand on an amplifier, since woofers require more movement. All of your low bass information is going to be going to your subwoofer, thus drastically decreasing the load on your AVR. Running the 12's crossed at 80 hz, will be presenting a load that's essentially the same as an A5's load to your AVR.
As myself, and others, have said before. If you were looking for a pair of speakers to do 2 channel listening with on your 605, I wouldn't be recommending the 12's. From what I've gathered though, your rig usage is almost exclusively HT. HT is nowhere near as demanding of audio gear as 2 channel is(generally speaking). The constant dynamic swing of music makes an amp work much harder than a movie, which is generally full of quieter scenes which put next to no strain on your amp, with brief dynamic bursts in between. This obviously isn't true of all movies, of course.