As you can’t have more than one iTunes library open at a time, trying to organize your music between multiple collections is a tedious, manual operation, with no simple way to compare your libraries side by side. SuperSync.
SuperSync is an app for Mac and Windows that lets you view your entire library and connect a second library on a hard drive, NAS, another computer running SuperSync, or iOS device. from there, SuperSync lets you compare, organize, merge, and manage your iTunes libraries across all of your Macs, PCs, and iOS devices. But does it work? According to this review from DJ tech Tools, sorta. Demo version available.