There are a few areas where you can do this. You should really try the manual, but here's a quick low down:
1. Program mode. Actually just velocity switching.The 2 osc can be partitioned such that the velocity of a key can switch between one program sound and the next. [menu] ->[basic]->[osc1]/[osc2]->[velocity sw L->H]
This'll help do what you want:
2. Combi mode. [menu]->[keyz]->[key zone]. You've got up to eight there.
3. Seq mode. [menu]->[keyz]->[key zone]. 16 here.
Some limitations on effects and voices due to polyphony and processing power, but overall quite a good synth.
