I just finished a discussion with a guy over on HomeTheater Shack over whether amps color sound.
He setup a mic ran his Focal Maestro Utopia's off two two different (powerful) amps and put up the result (
Do Amplifiers "color" sound? - Page 7 - Home Theater Forum and Systems - HomeTheaterShack.com).
While the scale is too large, and the graphs should have been overlaid, and while there should have been at least 4 runs (A then B then A then B) to eliminate other factors; the graph does show a difference.
And it wasn't in overall volume. They could be driven loud. They just weren't flat.
Thing is: I got him to try a more efficient and less demanding speaker and the differences went away.
I ran into the same things with my 801S2's running off a Marantz AVR. I had to move them to my Yammy pro-amp to get good sound. Then there's my 801N's which still have sound issues on the Yammy. Looking at their impedance graphs I'm not surprised.
I don't know the particulars: but there is more than wattage-to-spl involved here in the load a speaker presents to an amp.