The SD2 will give you a lot of the Ketron sounds, to combine with your Tyros sounds, thus expanding your sound combinations.

Downside:
The SD2 only has a volume control, therefore it relies heavily on a comprehensive Midi controller keyboard to get the best out of it, unfortunately Yamaha arrangers have some of the worst Midi controller functions out there, and so you will only be able to use the voices as is. (If you’re really interested have a look at the SD4, which is effectively 2 x SD2 with controls)

NOTE: You can buy external Midi controllers, (No keyboard attached) so if you added one of these you could then go to town with the combo.

Hope this helps

Bill