Hi John,
You can have the best of both worlds - buy a Ketron SD3 which is the SD5 in module form. Exactly the same but smaller and without the keys and speakers. Ketron modules work wonderfully through midi and you can play the Yamaha alone, the Ketron alone or the style from one with the sounds of both together. Gives you twice as many styles and twice as many sounds to choose from too.
Best wishes,
Tony - Sheffield UK