I own a S80 that is similar (99%) to S30 as you know. The plugins are not just sample ROMs but plug in synthesizer modules with thir own polyphony, insertion effects, editing software etc. Avoid XG100 and DX100 boards as they have some sortcomings. These two boards are made for older MU series modules and not new Sxx. You can buy piano 150PF and 150AN witch is a true analog synth in a board (same as AN1x) with its own computer based editor. Also you can buy the 150-DX board that is a DX7 in a box.

In my S80 i have PLG150PF (piano) and PLG150AN (analog) as most S80 users i know.

Avoid XG plugin due to its poor & thin voices. It sounds as a home toy-keyboard because its parts are assembled from just two sampled elements instead of S80 four elements parts. You need XG plugin only to playback computer MIDI /XG-GM files you have.

PS: S80 sounds really great and the pianos on PLG-150PF are of the best in the market today.