I have not used the MU128, but have used the MU100R. The MU128 has a GM Level2 sound set, which might be helpful for future midi file compatibility. The MU128 has 32 MB ROM, like the PSR9000, although I do not know if the sound sets are the same. It has three expansion slots for additional synth technologies such as vocal harmony, physical modeling, and maybe format synthesis. There is also a Piano board for it. It is also a midi interface for a computer. The display is cool, as it shows activity on 16 midi channels at once and shows an icon for the instrument selected on a channel of your choice.

I would concur with Freddy for studio work, Kurzweil 2600 is a good way to go, although the Roland 5080 is more to my taste. The main attraction of the MU128 would be the flexibility to explore new synth technologies at a more affordable entry price.

Clif