Are you only interested in SoCal? San Jose State is excellent for CS and also has a great music program, with both BM and BA options.
Combining a BM with a computer science BS is going to be a lot - BM programs are quite intense and don’t have much elective time to devote to a second degree. If you haven’t read the oft-recommended “Double Degree Dilemma” article, that would be a good place to start: Double Degree Dilemma essay (written by David Lane)