I don't see a reason why you can't use 80 dB. The absolute reference level you choose doesn't matter as much as getting all the speakers in the surround system to be equally loud.
When I first set the level on my speakers, I found that any lower than 75 dB would allow other sounds, such as the furnace/AC system or the refrigerator in the nearby kitchen, to interfere with the pink noise from the receiver. Set the volume high enough to be louder than those other sounds.