I'm in the combined MBBS program, but I'm not doing B Mus/MBBS. I do know the 3 girls who were accepted last year for this particular combo. Most of them are like you - want to become doctors but also passionate about music. I think one of the great things about the combined MBBS program at USYD is that it caters to students with a diverse range of interests.
The structure of all the combinations is this:
Yr 1-3 Bachelor of X (X being Arts, Business, Economics, Med Sci, Music, Sci (Adv))
You are basically just like any normal student in this degree. You need to follow all the course rules and meet the graduation requirement for this degree before moving on to MBBS. During these 3 years, you have to complete 3 courses which are mandatory for all combined MBBS students - communicating effectively in teams, medical research ethics and a research project.
Students in the degrees other than B Med Sci and B Sci (Adv) are required to complete at least one 1st year biology/molecular biology & genetics and one 1st year chemistry subject as electives.
Yr 4-7 MBBS
You study MBBS together with all the other students who were admitted through the graduate entry stream (meaning that they first completed at least a bachelor degree, attained a high grade point average and high GAMSAT score, and passed the interview).
One more thing which may be of interest - even though the $10000/yr Scholarship for Outstanding Achievement is usually only awarded to students who got 99.95 or more UAI (which is everybody in the arts and science combos which have a cut-off of 99.95 UAI), students in B Mus/MBBS (which has a cut-off of 99.5) are given a special combined med scholarship of equal value - so that's $10000/yr for the 7yr duration of the combined degree.