I have the 990 processor with B&W 804S speakers.
The 7125 did an OK job, but when I changed to the 7500 I noticed:
More detail in the music
Smoother highs
More defined bass (not muddy)

Those were the most noticable changes. I had it like this for a few months last summer before changing out my MIT brand RCA cables to Oracle 3.2 XLR. Once I did this, music became even more alive with detail and instruments had pin-point locations.

I know people that have spent thousands of dollars more for HT equipment (minus video) and most of them think my setup sounds better.
Why is that? They go blindly into a dealer and believe everything they are told without researching it first. Then they don't try other brands and take their time.