I cheated. I'll admit it. I am using the same ATC for two different swaps. (I think Leslie--my sister--is doing that also.)
My first thought for the music theme was my family. My parents were both music teachers and hard as they tried, they did get their four children to absorb a little knowledge. A few years ago during a family vacation we had a "talent" show. Leslie played a duet with Dad and I did with Mom. I thought those fond memories needed to be used for both of the music swaps.