For Sonos users who wish to choose which of their iTunes playlists are transferred to Sonos or for users who wish to use lossy formats for their ipods and lossless for their Sonos system. It makes a custom XML file on the NAS with unselected playlists removed and/or references adjusted to the lossless files. If you wish to only transfer a subset of playlists the application can be configured to display a playlist selector before the custom XML file is generated. The application can be configured to run and create the custom XML file on your NAS each time iTunes is closed.
I have written an application that solves two main issues for Sonos and iTunes users. Many people like to use iTunes to catalog their MP3 collection for use with iPods but prefer to store lossless files (perhaps apple lossless) on their NAS for use with Sonos. The "iTunes Music Library.xml" cannot be simply placed on the NAS as all the tracks are pointing to the lower bitrate MP3 files. Also many iTunes users have too many playlists to be imported into the available Sonos memory. (Especially if lots of smart playlists covering your entire library are defined)
My application solves the above two problems by changing the paths of the MP3's (or other lossey file types) within the "iTunes Music Library.xml" to the equivalent paths of the lossless files. It also allows the user to choose which playlists they wish to be imported into their Sonos system from their iTunes library. It also eliminates the need to maintain two separate iTunes libraries (although you are still required to create lossey and lossless copies of each track)
The application caches (and maintains) a one to one mapping between each file in iTunes with the equivalent higher quality file on your NAS. This caching allows the application to run through approximately 10,000 tracks on my PC and write an alternative xml file to my NAS pointing to the lossless files within about 25 seconds.
The application is completely configurable so it can be configured to match your setup.
More information, screenshots and the download link are above.