I just looked at the Marantz website and one thing on the 7500 that changed from the 7400 I do not like is that the 7500 has a rotary dial for inputs instead of individual pushbuttons. It's no big deal, I just like buttons better. I would imagine they sound very much the same and like you look forward to hearing from someone who has one. Maybe over Christmas break I will give my local dealer a call and see if he has one in stock. I want to audition the Monitor Audio Gold 10 speaker at his place anyway.
The SR5400 rated more than its advertised output with all channels running on the test bench according to homecinemachoice.com. Since the release of the 400 models, Marantz now guarantees a minimum of 70% output with all channels running to their listed specs.