keep in mind that upscaling faces a tough job in essentially trying to create something out of nothing. Either your display or your receiver will be doing the upconverting in any case, if you feel that the 606 does a poor job of upscaling, your TV itself may do a better job. I too have found that for non-HD signals, my 605 usually actually makes it look a little worse for trying to upconvert than it does straight to the TV. It's one of the caveats of the receiver, the main benefit being the one wire to display.
Also keep in mind you paid ~$300 for something that does so many things, whereas for a pure upscaler you would pay at least $500 for.
