Thank you for your reply.
Just to clarify, all of these playlists were originally created within iTunes, and then subsequently "disappeared" after an update from Apple at least two or three years ago. I thought they were truly lost. I discovered that they apparently still live on my iMac (albeit in some hidden--at least to me--location). I made this discovery while using the third-party app Vox. All of these playlists are visible in Vox under their "collections" tab. I can export them from Vox, but the export puts them in xpsf format.
So the real question is two-fold: 1) Is there a way to import an xpsf playlist into iTunes (so far, the answer seems to be "no," OR 2) Can you or another user point me to where these old iTunes playlists may be hidden on my iMac. I have seen some forum posts suggesting that they are in an ".itl" file--the issue here is that I've been in the iTunes universe for quite some time and have a number of old iTunes libraries on the HDD.
Obviously, I could rebuild these playlists, using the lists from Vox as a guide. But that seems rather tedious and labor-intensive if there is a straight-forward way to simply get the original playlists restores to iTunes as a digital maneuver.
Any help much appreciated.