I purchased the 773 a few weeks ago when Newegg ran their sale for $480. Last week Amazon had the 673 for $380.
I think the only difference is the $80 WiFi dongle, banana plugs for zone 2, and the second HDMI output.
Hooking up the WFI was a real pain. I had to re-set the dongle (right out of the box) and program it manually. WPA did not work.
Updating the software to 1.46 over WFI was useless. I used a thumb drive to finish the job. (Scary when the black box becomes a brick)
Now I have internet radio and can access my laptop's contents. PS3 does it better, IMO.
Their vTuner website works like a charm and I have bookmarks on the internet radio stations. I found WBRU is Boston. A station I grew up with.
This is a great rerceiver.