I tend to agree what most of the folks are saying here. Skip the converter idea and just get a new receiver with pre outs and do things the correct way. Don't getto rig your system with a converter system.
So it seems...
Check out accessories4less and pick up a refurbished Onkyo. Most of them have had nothing wrong with them and where returns from customers who didn't like them for one reason or another. They come with a full warranty as well. You could also look at the Marantz line. You could also wait a few months and get the Onkyo 707 when the 708 comes and they start going on sale. You could also get the Yamaha 665 for 499 or less which has pre outs.
What if I wanted to go the pre/pro route, instead of a receiver...is there a multichannel processor you would recommend? What about the Onkyo Professional processor? I know that thing's a beast, and it's expensive...is it worth doing that or going with a more reasonably priced AVR with preouts, and then adding the amp?
As far as external amps. Go with Emotiva. They offer the most bang for the buck. The UPA-3 would be a great amp that would give your Polks all the power they would ever need.
I've been hearing great things about these amps...the UPA-3 is the three-channel model, yes? Would you recommend doing this, that is, amping the front stage (three channels) and letting the AVR amp the surrounds, or do you think I should get a five, six or seven-channel amp and let it power all the speakers?
As for Emotiva, what's their story? It seems like this brand arrived on the scene and just exploded like wildfire; when did they come on the market? Did they do something before amps? What has made them so popular, besides price?
I know they have a MASSIVE bang-for-the-buck reputation, but do their power ratings equal what they actually put out, more or less? Are they really as powerful as their numbers suggest?
EDIT: BTW, on Emotiva's site, there doesn't seem to be any "UPA-3" model...did you mean this:
http://emotiva.com/xpa3.shtm
...the "XPA-3"?