I KNOW THERE ARE SEVERAL GUIDES ABOUT THIS. BUT I FOUND HOW TO DO THIS WITHOUT GUIDES. I'M GOING TO WRITE EXACTLY WHAT I DID.
First you need Multiman 1.16.9+ (there are two methods in doing this. the first one is fps. I'm going to tell you the USB method) remember that you can only add one music file as the custom music
1. install Comegenie's Awesome File Manager on your jailbroken 3.55 or less. can be found here http://www.comgenie.com/filemanager/
2. find your mp3 file and name it "SOUND.BIN". the mp3 can't be more than 192kbps
3. copy "SOUND.BIN" to your usb
4. Navigate to this directory: dev_hdd0/game/BLES80608/USRDIR/ and delete the "SOUND.BIN" it contains
5. copy your original "SOUND.BIN" from usb to dev_hdd0/game/BLES80608/USRDIR/ via Comegenie's Awesome File Manager
6. load Multiman
congratulations! you have added your custom music
First you need Multiman 1.16.9+ (there are two methods in doing this. the first one is fps. I'm going to tell you the USB method) remember that you can only add one music file as the custom music
1. install Comegenie's Awesome File Manager on your jailbroken 3.55 or less. can be found here http://www.comgenie.com/filemanager/
2. find your mp3 file and name it "SOUND.BIN". the mp3 can't be more than 192kbps
3. copy "SOUND.BIN" to your usb
4. Navigate to this directory: dev_hdd0/game/BLES80608/USRDIR/ and delete the "SOUND.BIN" it contains
5. copy your original "SOUND.BIN" from usb to dev_hdd0/game/BLES80608/USRDIR/ via Comegenie's Awesome File Manager
6. load Multiman
congratulations! you have added your custom music