Bernie,
You might want to consider a Korg Microkey Air. I have the 37, 49, and 61 besides the MicroArranger. Even though the keys are of the same size, I find it much easier to play the Microkey series than the MicroArranger. The MicroArranger is almost 35" wide and 11" deep, while the Microkey Air 49 is a little over 27 inch wide and only 5 inch deep. Very slim. A USB cable will connect the Microkey Air to your SD40. Also, if you don't have the Korg Legacy bundle software, I think any Korg Microkey Air comes with it. I will say the bundle software alone is worth the price.

Chris