If you read about the old time kung fu guys, they always recommend "scholarly pursuits" such as music, calligraphy etc.

It seems obvious that if you can gain a grasp of rythym thru music, you could apply that knowledge to martial arts. There are the chinese stories of many martial artists also being members of opera actors in old time china.

I think the idea of music opening up a different part of the brain might be just as important. Different subjects use different parts of the brain. If all you do is fight, you only ever use the fighting part of your brain. If you play music or learn other things, more of your brain opens up and you can apply that to the kung fu.

Music has psychological effects that are obvious so a knowledge of that might be good for kung fu. If you know which music evokes fear or paranoia, you could imitate those sounds to invoke fear and paranoia in an opponent. That is how some people "psych out" other people. They use their voice like a musical instrument and play whatever "music" evokes the desired emotion in the other person.