No official information but surely more expensive.
Official is: Better vocal harmony, USB port as PSR 3000, no built in floppy drive but option to use an USB floppy and of course better voices.
No infos about CD writer, MP3 playback, but I don't want to pay these features.
I noticed, I'm quoted in another forum (because the people posting the psr-world link, said "German" because the language, but Germany's Yamaha forum is Yamaha.de Forum )

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Regards
RF