My Cable box does the upconverting for me, I watch 4:3 shows in 16:9 all the time but I have also found the scaler in my 3808 to be acceptable as well. Most of the new avr's out there have pretty good processors in them now, I doubt you would find the PQ unacceptable from any one of them.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70