On Nabokov and Music, the top authority is Boris Katz. Unfortunately,
much of his work in this area is still in progress, and the things that
have come out are in Russian. They need to be translated--or everyone
needs to learn Russian (I vote for number 2! Help save a Russian
program today--sign up for Russian courses!)
Here's one available on line; section 4 of the article is about music
in Nabokov's The Gift.
http://magazines.russ.ru/voplit/2005/5/ka26-pr.html
Stephen Blackwell