We haven't BTDT, but we have looked into it. Have you considered finding someone who does music therapy instead of music lessons? I have been told that with traditional music lessons the child is expected to conform to the teacher's methods, but with in music therapy the teacher/therapist adapts to the student's ability and needs.
Gena
DS, age 11 and always amazing
“Autistics are the ultimate square pegs, and the problem with pounding a square peg into a round hole is not that the hammering is hard work. It's that you're destroying the peg." - Paul Collins, Not Even Wrong