Finishing a Degree
You should check out the services' ROTC programs - "Green to Gold" is the US Army's program. It is available for junior enlisted members with some college to attend long enough to finish their degree on full scholarship, while earning E-5 pay (last time I looked). Of course, like the full ROTC program which you might have checked into in high school, the degree program has to be approved by the service, so a Music Theory degree will probably not be available.
Check into Green to Gold (or the other services' variants).