Try going to your MC 32 library, probably located in a file path similar to this: C:\Users\username\AppData\Roaming\J River\Media Center 32
Then copy playlistx.jmd, and paste that into your MC 33 library (located in a similar path) - MC will warn you that this will overwrite that field, but since you said you have nothing but empty playlists in MC 33, I presume that should not matter.
While I have not used this technique on playlists specifically, I have used this approach several times when I accidentally overwrote a whole bunch of files with the same value at some unknown previous point in time. Since I had done a lot of recent tagging that I did not want to lose, this is how I solved it. If I had restored the entire library, I would lose all that recent tagging work. But you can pick and choose specific fields from a backup or an earlier install, and then overwrite the current library with that specific field - it is just not an automated process.
Of course it goes without saying, but I'll say it anyway, perform an MC backup on your existing MC 33 library prior to doing any of this in case something goes wrong.
Hopefully the above will do the trick for you.
