F both your libraries contain the same music at this present time, I would just dump it up to your server/NAS and then sync it back to the computers. Test it out with some dummy files... Here is the command I would use
robocopy.exe /S MIR x:\sharedItunesLib "c:\documents and settings\userName\Desktop\testDir" /LOG+:c:\pathToStoreLogFile\file.txt
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ROBOCOPY v 1.96 : Robust File Copy for Windows NT
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Started : Wed Jan 07 20:10:21 2009
Usage : ROBOCOPY source destination [file [file]...] [options]
source : Source Directory (drive:\path or \\server\share\path).
destination : Destination Dir (drive:\path or \\server\share\path).
file : File(s) to copy (names/wildcards: default is "*.*").
Copy options: /S : copy Subdirectories, but not empty ones.
/E : copy subdirectories, including Empty ones.
/LEV:n : only copy the top n LEVels of the source directory tree.
/Z : copy files in restartable mode.
/SEC : copy SECurity info (both source and dest must be NTFS).
/SECFIX : FIX SECurity info on existing files and dirs.
/TIMFIX : FIX TIMestamps on existing destination files.
/MOV : MOVe files (delete from source after copying).
/MOVE : MOVE files AND dirs (delete from source after copying).
/PURGE : delete dest files/dirs that no longer exist in source.
/MIR : MIRror a directory tree (equivalent to /E plus /PURGE).
/A+:[R][A][S][H] : add the given Attributes to copied files.
/A-:[R][A][S][H] : remove the given Attributes from copied files.
/CREATE : CREATE directory tree structure + zero-length files only.
/FAT : create destination files using 8.3 FAT file names only.
File Selection: /A : copy only files with the Archive attribute set
/M : like /A, but remove Archive attribute from source files.
/IA:[R][A][S][H] : Include only files with some of the given Attributes set.
/XA:[R][A][S][H] : eXclude files with any of the given Attributes set.
/XF file [file]... : eXclude Files matching given names/paths/wildcards.
/XD dirs [dirs]... : eXclude Directories matching given names/paths.
/XC | /XN | /XO : eXclude Changed | Newer | Older files.
/XX | /XL : eXclude eXtra | Lonely files and dirs.
/IS : Include Same files.
/MAX:n : MAXimum file size - exclude files bigger than n bytes.
/MIN:n : MINimum file size - exclude files smaller than n bytes.
/MAXAGE:n : MAXimum file AGE - exclude files older than n days/date.
/MINAGE:n : MINimum file AGE - exclude files newer than n days/date.
(If n < 1900 then n = n days, else n = YYYYMMDD date).
Retry Options: /R:n : number of Retries on failed copies: default is 1 million.
/W:n : Wait time between retries: default is 30 seconds.
/REG : Save /R:n and /W:n in the Registry as default settings.
/TBD : wait for sharenames To Be Defined (retry error 67).
Logging Options: /L : List only - don't copy, timestamp or delete any files.
/X : report all eXtra files, not just those selected.
/V : produce Verbose output, showing skipped files.
/NP : No Progress - don't display % copied.
/ETA : show Estimated Time of Arrival of copied files.
/LOG:file : output status to LOG file (overwrite existing log).
/LOG+:file : output status to LOG file (append to existing log).
