rikkisbears,
1) No, not sound module -- I like to play 2-manual (2-keyboard) instrements, like classic organs.

2) Yamaha have styles "one touch" voice presets. It very convinient to pick up e.g. "cha-cha-cha" on both arrangers and play vivid style from Roland and cha-cha-cha voices and effects prepared by Yamaha. Usually it perfectly fit. If I will have sound module, I should choose voices and effects by try and errors for every style. It will be very time consuming.

Thus I was not changed my PSR9000 for Motif or Fantom yet.

For me good presets is 50% of arranger overall value.