Well, I think I've got to the bottom of the problem.
On http://littlebits.cc/projects/get-your-bach-on-with-the-arduino-midi-organ
the guy admits
(a) His blog Arduino sketch no longer compiles after some considerable period. Nothing in the blog to warn the unwary.
(b) He now says it is coded for the Leonardo, despite the fact the the word "UNO" is splashed all over the sketch. ("Leonardo" turns up as a footnote in a comment about 80 lines fown the code).
(c) He says "I tried compiling the code with the board "littleBits w6 Arduino Module (Leonardo)" and got an error in the build process itself, i.e., the tool chain has a bug. I've had problems like this with UNO, too. Board definitions don't always seem to be in sync with the tool chain."
To me, this has all the hallmarks of a disastrously unstable environment. As I've said elsewhere, Atmel ought to take the situation by the scruff of the neck if they want to avoid adverse reaction. It's a fantastic product, but so frustrating when sketches fail to compile, even when the post is only 2 weeks old!!! I am beginning to wonder if I should go back to Zilog . . . .
Having had a good moan, is there any chance that the code could be re-written for an UNO? I see Sparx having some success but don't know what edits he did. The chance of having 5 notes playable is very tantalising!