I got the PF (piano) plug-in board with the S-80. Honestly, I don't think it offers much above the sounds on the S80 itself. Check it our for yourself before you buy it. Lot of EP sounds, not too many different "grand piano" sounds.

I like the first piano sound on the S80 the best (A01) which is a stereo grand. Of course, there's a lot of capability to edit the individuals sounds more to your liking as well. I haven't got to that yet. Any other S80 users edited piano sounds to get something more to their liking. If so, how?