I use the Shure SE 210 and the sound of the N9 is quite good. Verry crisp, yet a bit flat from time to time. But good overall.

I was thinking of an EQ as well and tried sigma player. I didn't like the UI and the sound of the provided EQ so I stayed with the stock player.

I tried to play around with a command line EQ, called alsaequal which would work well with alsamixer (wich is installed, try calling it in the shell). Unfortuantely it needs to be compiled on the n9 and I did not manage that (at least on PR 1.1) due to dependencies and Aegis (i guess). I started a thread a while ago on here, please feel free to investigatre on that topic as I am still verry interested yer have not so much time right now.