The only way that I know you could do this that would work is to replace your engine sound with the music... You would no longer hear the engine running while you were traveling in the panzer.
You would need to convert the mp3 to a .wav file...
Goldwave is a sound editor that is shareware... I use it as do a number of others in AH... I even think mitsu uses Goldwave.
It is very easy to convert mp3's to .wav's with Goldwave...
Hope this helps some.
BOOT