I don't think there's a reason to be concerned here. What you're measuring is the result of the combination of receiver, speakers, and room. It has nothing to do with whether the amp is really 120wpc---it's not putting anything approaching that out at 75dB.
By comparison, if you went with high-end Klipsch speakers in a very live room, you'd probably have over 75dB.
If you really want to have reference levels at 0dB, then adjust the levels on the mains to achieve that. A good processor *shouldn't* start clipping within the range it allows you to adjust each channel.
Bruce
