Well no one answered this so let me, even though its been quite a while. My son got the QRX-4500 a year or so ago. I assume its the same but with more power. HIs is a jewel. It was rehabbed by the shop we bought it from. The one drawback is the decoders. They are early generation, meaning 3db of separation in some directions. So it sounds great, although SQ/QS performance is rudimentary. I thought about getting him a plug in full logic SQ Sony decoder to run with it but the deal fell through. But with that one caveat, a healthy one of these is a good unit!
Power ratings are almost identical with the 4500 being advertising, from what I've read, having 1 watt more in quad mode.
I've been running mine in the bedroom for a few months and I love it. Mine has issues with the tuner dropping out every so often
then coming back on after a few mins. I'm not a fan of radio these days anyways.
The decoders every so often get loud static, I'm not sure if these units have the cold solder joint problems like the later big boys,
but I use the Involve QS board instead most of the time.
This is the loudest 22W I've ever heard in my life. With some big woofers, no need for a sub.
These early units are great if you can find them cheap and in good order.