S30 & S80 can be GM using the PLG-100XG plugin that gives them XG/GM capability with card's own XG sounds and polyphony.
I disagree with previous posts that Roland's expansion boards are better than Yamaha's.
Roland's boards are just sample ROMs and nothing else. Yamaha's PLG boards are standalone synths with different synth engine each one of them, their own insertion FXs, polyphony, editing software & paremeters, midi extra channels etc.
For example there is a full (and better) DX7 plugin, an analog synth, an harmonizer with its own source input, a physical modeling synth etc.
You can have, as an example, a S30/80 synth with two of those boards and 128+ voices, 32+ parts, up to 16 IFXs, three synth engines, three sound computer based editing modules.
In a few words:
A Yamaha ROMpler 64 voices etc.
A fat 6-voice analog synth
A DX7
All of these in one excellent keyboard.
Think about it...