It is theoretically possible, by creating a weapon with a very short lifespan and no damage rating and having that weapon play the music you want. However, this method is not very practical. If the song were set to loop at a certain point, the player would have to fire again every time the song stops. Sure, you could set the weapon to loop the sound effect, but the weapon would have to be fired almost constantly to keep the sound going. Sure, you could also have a ship that continuously follows you (like on a mission) that fires the weapon, but that is also not very practical. Besides, even at 8bit 11khz mono, a complete song would take several megs to hold.
Of course, I'd love it if, in a future release, the ability to have music playing during the game would be nice, I don't see it happening anytime in the near future.
PS: You could just use the Apple cd audio player to play an audio cd while you're playing EV/EVO, but everytime the track changes, you would have to bring up some dialog box to let the track change.
And now, if you will excuse me, I think I've used my daily allotment of rambling space...
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Knucklehead, Aeon Productions
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(Insert witty remark here)