As mahansm points out, the 990's volume information is unrelated to the power output being generated by the amp.
I don't know of any practical or useful such meters. It's not a direct measurement of the 7500, but some power conditioners include a readout of the amps being drawn at any given time. As an example, when playing a movie in my system at relatively high volume, I've seen the draw exceed six amps. Six amps for the entire system, which would suggest that at least with my speakers and in my room the 7500 still has a lot of headroom to spare.