As far as I can tell the only differences are THX and the PC Input.
Also, from the TX-NR609 manual, the PC Input has the following note:
Available resolutions: [640 × 480 60 Hz], [800 × 600 60 Hz], [1024 × 768 60 Hz], [1280 × 1024 60 Hz]
So, IMHO, it's worthless as a "PC Input". I guess it could be useful to hook up a laptop that lacked HDMI for a temporary input. But, with those resolution restrictions, it certainly isn't something you'd want to use everyday. HDMI is clearly the better way to do a PC Input. However, the real value in having the PC input is that it gives you another assignable input that you can use for HDMI.
There's also some talk about the TX-NR609 supporting wireless. It appears to use a little dongle called a UWF-1. However, since the TX-NR609 only has the same front panel USB as the RC360, you'd have to plug it in the front. So, if you wanted to plug a USB device (USB drive or iThing) into this unit, you'd have to unplug the dongle (and lose networking). Or, maybe you could hang a hub off the front. So, if I needed wireless, I'd probably be looking at going with a wireless bridge with either model.