Spanning from a backed up iTunes library
I backed up my itunes library from an old computer onto an external hard drive. I have another computer now, but the library is too large to move onto the new computer.
If I press option when starting iTunes to load the .itl file on the external hd and select that same library in TuneSpan, I can span as normal. However, when the computer is not connected to that hard drive, that .itl file is not available; so iTunes must load a local .itl file and then the music I spanned from my external hard drive is not accessible in iTunes.
How do I span the content I want to keep locally to my computer while leaving the majority of my content on my external drive?