You're still gonna have to tune the TV with it's internal tuner unless you invest in a stand-alone HDTV tuner and,eve,tne, you'll still have to use it's internal tuner to select your stations.
But, with the external HD tuner you could feed it's output through the AVR and from there to the TV.
As the other guy said, until they start marketing AVR's with built-in ATSC HD tuners, you're outta luck.