You are obviously a lady that is up for a shape challenge....My immediate thought for this would be to make an upright piano shape cake (like the old ones), cover it in light brown fondant and then paint it in a 'scrumble' style (not sure if you have that expression where you are). It's like a wood grain effect. The keyboard you could obviously do in white and black fondant. Then to add the personal touch, where you would normally have the piano maker's name on the front, put the name of the birthday boy instead. If you have time, maybe even a piano stool from fondant, with chocolate fingers for legs.
Whatever you decide, will be very interested to see what you come up with, so don't forget to post a pic!