I have trialled an app from Mark/Space called "Missing Sync", which has the great advantage of not requiring a cable to work; it uses Bluetooth or Airport, and is Mac-compatible. There is a Windows version. Missing Sync is free for a while, but must be bought. Price is not cheap, so if anyone is looking for freeware, look elsewhere. It is very good, and does not duplicate files, which DoubleTwist does. Despite workarounds, the DoubleTwist dupe problem will recurr eventually, so while I have used it in the past, I have decided to pay for Missing Sync and be done with it. Missing Sync has also recognized that Apple has removed the DRM protection from music files I have upgraded thru Apple, and will let them mount, which DoubleTwist does NOT.