Well me and a friend looked at the sounds and stuff of the client and we figureed out how to add mp3s to a client step by step info on how to add mp3s.
1. download a song thats an .mp3 file from an mp3 site heres 1. Http://www.beemp3.com
2. search on google mp3 to Wav converter and use it to convert an mp3 to wav file.
Link: http://www.convertmp3towav.com
3. after that goto your eo client where ever its at and and goto the sfx folder and rename the file u got from the convertion ether gui,har or sfx and copy one of the files for example sfx037 these are wav files test the sound before replacing with the song u want cause you may want to know what
thing on eo you want the song to start up for like warping to a map.
4. once replaced open eoclient and test it out
let me know if you have any problems or if i need to change anything in the guide let me know =D.