Wow, 2 Doods---that looks wonderful. I would go with the red on red on the back---something simple since there are so many wonderful things on the front.
p.s.----I did the same thing and have bought 3 different fabrics for a quilt I'm working on for the back---like you, just couldn't decide

That makes sense to go with the black and white, since the parents are into piano.....would definitely go with flannel backing...and red would be appropriate....