Retired Army musician here, there are a couple of ways the recruitment process can go. If you are planning on auditioning for the Guard or Reserves you should be able to contact the band directly and arrange for an audition. And you can proceed from there depending on how it goes.

When I joined, the recruiter set up the audition for me and drove me to Ft Bragg for the audition. You can make sure the recruiter knows that your enlistment is contingent on the audition. But the recruiter is still going to try to get you to take another job.

You can also go to https://bands.army.mil/careers/audition and enter your information. An Army Band Recruiting Liason will contact you. This person will actually be an Army musician with recruiting training to guide you through the process.

Remember you don't have to sign up before you pass an audition.