I'm by no means an expert on how the game files work, but I imagine that if the audio files were replaced they'd likely play the modified audio while using the visual effects from the original song. And yes, part of the draw of the dubstep gun is the visuals syncing with the audio, but if you just wanted the gun to play a different song and were not worried about the visuals, that would likely be entirely doable by the method Bloodjack mentioned.That wouldn't work, each song has specific flags as for when it should fire the pulses, so without the ability to update those, they won't behave correctly.
Take a bullet-laden trip through musical history! Get the crowd off its feet with the power of polka, set those hepcats a-swinging with big band, indulge your refined side with some classical, and then start the moshpit with some heavy metal.
while having fun with the game files I came across the sounds used for the dubstep gun.
There is actually 3 .ogg files for each guns.
sounds_common_XXXX.ogg : less than a second long, it's the part of the music when you press the trigger but it does not inflict damages yet.
sounds_common_XXXX~Song_Start.ogg : the actual hurting part. more or less 28sc, loopable.
Sounds_common_XXXX~Death.ogg : the sound played when you release the trigger.
So yeah, you can already replace the music if you want, I guess... You have to create those 3 files and replace them. (<--- total theory !)
I suppose its worth noting that the recent Dubstep Remix DLC added a death metal track for use with a new dubstep gun.
http://store.steampowered.com/app/247293/
Take a bullet-laden trip through musical history! Get the crowd off its feet with the power of polka, set those hepcats a-swinging with big band, indulge your refined side with some classical, and then start the moshpit with some heavy metal.