I'm curious to hear your impressions (you too ImcLoud). I'm starting to look at separate amplifiers, but unfortunately my current receiver has a little design flaw: it features pre-outs, but no main zone 12V trigger nor a switched outlet to plug an adapter into. As I'm not inclined to leave a power amp running idle 24/7 wasting electricity, and well...I'm lazy, I may look to replace the whole spiel.
Also curious to see if Emo is going to release a XPA-500. I don't necessarily need something as powerful (and large/heavy) as the XPA-5, but I don't foresee the UPA-500 representing a big upgrade from what I've got either.
Fun times!
There are ways around the lack of 12V trigger. A triggered power strip is often recommended on AH. I have no experience with them myself, but if you search or bring up the question, you will get some recs.
Also, some amps do have a mode that will kick it on when it gets a signal (not a 12V trigger). But, I could see how that could be more trouble than it is worth.
Finally, NEVER plug an amplifier into an outlet (switched or not) integrated into your receiver. They aren't rugged enough to supply the power that the amp will need.
All that being said, upgrades are nice if you have "a legitimate excuse".

I found my first possible legitimate excuse the other day when I realized that my Pioneer Elite doesn't have a front HDMI port.....not time yet, but gets the gears a-turning.