That doesn't really help the OP.
I have a similar problem, the radio djs are far, far, far louder than the radio music, to the point of making the radio stations essentially unlistenable. I haven't found a solution yet.

I came here looking for a solution to the same problem, the radio DJ is loud enough so you could hear him through earplugs and yet the music itself you need to put the volume up to max and hold it the speakers against your ears to hear the music.. by which time the DJ come back and blows your eardrums out and shatters all the windows on the street while setting off every car alarm. (ok maybe a slight exageration but you get the picture)
All settings in game are at maximum.
The only thing Ive read thats a possible solution was on NMA:
"My Realtek drivers were set for 5.1 sound properly, except that there was a "speaker fill" setting that was unckecked and this little setting apparently turns stereo-only signal into 5.1 signal.
So yeah, everything (ambient sound, footsteps, dialogue, radio announcer) was working fine except the radio music.
So, if you have a Realtek you might want to check that setting and even if you don't.... there might be a similar setting for your sound card too. "
I dont appear to have that setting or similar.
BTW thats on PC.. I really dont know why it would do it on an Xbox unless you got surround sound or something.
Edit: lucky for you guys Im into fixing things myself so went to look into what the problem might be. Alt-Tab was revealing enough to show FDDShow in the task bar.. so I promptly went and unistalled K-Lite Codec packs. Ran NV again and violla! music at the right volume (you probly didnt notice it before either but theres music on the splash page and in game menu too that was so qute you could barely hear it). So if your on the PC uninstall the codec packs, you shouldnt need them in most cases anyway.