Yeah - background applications be it winamp or itunes don`t slow down the game. I got a feeling most of our staff prefers to run some custom music in the background - after all thousands of hours with the vanila game music gets old...
So one option for you guys would be to turn the game music off and run your own stuff in the background.
But here`s a better idea. Most likely we`ll leave DoF music folder as easy to mod as it is right now. You just dump your .mp3s into Dawn of Fantasy/Music/ folder. Some for the battle tracks, and some for the peace tracks. Atm we have to rename all the music files to Combat-002.mp3 or Peace-011.mp3 e.t.c, but thanks to your feedback we`ll try to include a feature to save you this step. Just add your .mp3s to Peace or Combat folder - and that`s it.