I have taught music to an autistis boy and have an aspergers child - not an expert but african djembe drum + buffalo drum ( or other deep drum were the favourites for the autistic child I teach but he had to play with a beater rather than his hands)

I play the appalachian dulcimer and that was also a hit when on his knee and I played - he liked the vibration but couldnt co-ordinate hadns - he absolutely adored creating his own music on a computer using black cat ( he's 8) and we had a music session with the local music school and trombone and clarinet were a hit too

My own aspergers son doesnt like intruments to play but is really into rap music - hope this helps

Sue