Hi Harrymax
The SD 2 is the SD 5 with the arranger section and all controls and keyboard taken away.
The SD 2 will give you the sound you want, if you can successfully control it from your keyboards via Midi, as the SD 2 has no controls on it apart from volume. (If you just want to play single sounds then there should be no problem, but if you wish to mix and match then you are totally reliant on your existing keyboards capabilities)
Hope this Helps

Bill