A "FID" is just a file, eg. an .mp3 track or a playlist. On the player's drive(s), they have their own fids directories.

So just count those to see how many.

The set_max_fid program (written in C) is available (I'm attaching it here), but you may have different issues. Really, try and find the long threads here that deal with managing players with loads of FIDs and large drives.

Cheers