Good work on the script!
Use:
replace "\"" """
or
replace "\"" "\\u0022"
That works perfectly.
I must confess that i don't know why I have included the replace "\"" """ line in the index part of my script. It doesn't seem to help anything. I did a few tests about quotationmarks but had the impression that itunes doesn't have this character in ther music database. They use only single quotes there, which avoids the problem.