I think he is looking for something to improve the rendered quality of the midi sounds -- like the ketron sd2 or something like that..
Well if he's after that I have a like new SD4 for sale.Selling it for a friend who already had an SD2. He didn't realise that the sounds in the SD4 are the same and he didn't need the extras in the SD4.
The SD4 has the same sounds, but some cool additional features. For one, if you have a woodwind controller, you can use it without a laptop. Also, you can "layer" sounds, like trombones in 4ths, or Bari, tenor, trumpet playing 1,5,b7 for chord shouts. It's a lot more expensive, but worth it for those features, IMO.