Using the auto Eq on the Yammy 2500
Choosing one EQ setting over another should slightly change the sound you hear by sending slightly differently modified signals to your speakers. If you change the setting on the amp and you don't hear any appreciable difference from the speakers, then the exact setting you use is not pertinent to your ear using your sound system in your specific accoustic environment.
I set mine to "flat" as a starting point and have been listening there - in a while , I will set the amp to one of the other settings, and see if I can hear the difference and if it is better or worse to my ears. I don't expect the difference to be too large, however, as my speakers are relatively balanced.