I agree with bestbang4thebuck on the approach. Start with the 7125 and see if you're happy with its performance in your setup. If you are, keep it. If you're not, send it back and get the 7500.

I started with the 7125 as a potential upgrade from my Classe CAV75 driving my Martin Logan reQuests, a difficult to drive speaker. It sounded a tab better but still sounded compressed, which was my long standing issue with the CAV75. I was able to do a back to back between the 7125 and the 7500 and there was a dramatic difference. The 7125 went back and I'm very happy with the 7500.