We have communicated previously about this but just want to say that since your musical activities are hardly represented in the common application itself (or not at all?) i think a supplement is a good idea. However, I would call admissions and ask them questions about what is preferred. For instance, they might really appreciate it if you cue the best three minutes of your playing. Also tell them that the part is a solo but others are playing on your recording, and make sure that editing is not needed (I don’t think so, but check). Include a resume and/or repertoire and letters of recommendation from someone who knows you and your playing. Colleges care about work ethic, how you work with others, character in general- as well as your ability to contribute on campus with your musical abilities.