Unity and music tracks - load track at certain point and fading tracks in and out

I was wondering about using music tracks in my game. I want there to be a melody track for my game which plays by default. For this, I assume I just need to attach the music track to an object and set it to play? Or is there another way of doing this?

My game is a puzzle game involving moving objects however, and I would like a percussion track distinctive to each object to be played when it's being moved. This would obviously need to match up with the melody in terms of where in the song it is. The only thing I can think of doing to make this work would be to have all the percussion tracks playing, but muted, and raise the volume of the relevant track when it's picked up. However, this seems like it might take a little too much processing power, and I was wondering if there was a way to instantly start a song playing from a certain point in it's time signature, relevant to the main song.

Thanks for the help!