I'm a very avid music listener and I've tried several varying quality headphones with many different players on my phone (now to include MX Player). I will have to say that I too lean toward PowerAmp. MX Player does sound good but it isn't a true music player and will not do, but I will also say that I didn't hear much (if any) difference in the sound of PowerAmp and MX Player. Some file actually sounded better with PowerAmp IMO.
To defend the EQ, the EQ should not be used to compensate for you music but rather your equipment and personal taste. All equipment, be it a phone, mp3 player, headphones, etc., have "flat" spot in their sound signature, the EQ is used to compensate for those. It is an essential audiophile tool, that is why they make EQ's and DSP's.