I did the ICMP higher diploma, and then the BMus.
Both are excellent.
The higher diploma is essentially the same as the first year of the BMus.
I did audition for BIMM, and got an offer.
A friend of mine did 2 years at BIMM on their BA, he transferred to ICMP for his final year, and he says that ICMP's course was far a far, far higher standard.
I owe ICMP a lot.