Jemplode actually kinda does this already. Edit copy a playlist (or an entire playlist tree) in Jemplode, open a new window connected to another player, edit paste, it works. It would copy over an MP3 file if necessary, but if only playlist changes were needed, it would only change the playlists. It uses the RID feature to calculate duplicates, and off it goes. Magic.

Only problem is, Mike never optimized or fully debugged that bit, and it chokes on extremely large lists. Also, for players where there weren't any precalculated RIDs, you needed to generate them.

There were also some command line tools to do this, but they were tricky and only worked if the moon was in the right phase.

I was trying to do this sort of thing to keep my Rio Central and my Empeg Car in synch. It was very iffy. Now I just keep them equally updated by hand, the old fashioned way.

Anyway, for the purpose of transferring a dual-30 player to a single-250 player, the drive copying as described in the Disk Upgrade Guide is faster and more straightforward, and nothing has to touch the local PC, it all happens inside the player. The situation you describe where you want to synch up different players, that's a different issue.