Many thanks for your assistance John. I would say that anything louder than -16 places the unit in danger of going into standby mode. More bass, or turning the bass up, makes it worse. As far as how long it takes - *usually* it is rather fast, within seconds of cranking it up past -16 db. I have listened to nearly an entire CD at this volume however without it kicking into standby, but this is rare. Generally the AVR520 does not have nearly enough time to even get warm before it goes into standby mode. I have not tried listening to it for extended periods at low levels however. I suspect that at lower levels it won't happen.
BTW I got the unit at BrandsMall.com for $630 shipped if this makes any difference. The service was good and the unit was shipped quickly but I've never dealt with them before on a problem item.