Have a look in the YEM manual chapter "Special features for Tyros5/Genos".
It's more limited and fiddly than you think, though. You can't actually mix voices together, what you can do is select individual elements from the preset voices and combine them together. You can't select elements from SA / SA2 voices, and you can't copy effect settings.
You'd be better off just using a registration with R1 and R2.