Looking for an app to manage an archived music library
iTunes will actually let you use multiple libraries if you want, and then can switch between them on launch. So if disk space (and just keeping the files where they were wasn't an issue), you could use a second library. 

If you launch iTunes while holding down the Option key on your keyboard, you will get this dialog. 



You could choose 'Create Library' here, and make a second library. 

Unfortunately, the storage location of your music is a iTunes general setting versus per library. But, there is the options in Preferences -> Advanced to not copy files into the iTunes Media folder. Changing this though would affect your main library too though.