Are you sure that your song cache has customs in it? I just fired up Setlist Manager and it seems to be working for me. I have 2,950 songs including customs.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!