This is hard and I don't have anywhere close that I can audition them.
From what I can tell the upgrade to the RX-A720 from the RX-V673 doesn't seem worth it. The RX-AV820 adds multi-point YPAO which may be worth somrthing. Still the YPAO frim what I understand doesn't equalize the sub,
The Audessy seems to be the way to go versus the YPAO, but that said the Denon amps don't get as favourable reviews as the Yamahas..
I need to look some more into Onkyo but I was put off by some problems on the threads here & scouring thr internet. The TX-NR717 would be in my price bracket, but the 818 is certainly a step up price wise and with the reported issues I am worried I willl regret it.
All in all I keep coming back to the RX-V673..