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

Thanks Rikki and Chris. I don't know how I picked up the wrong dimensions, but I did. This changes the name of the game. Back to the drawing board. The Korg Microkey Air, being so slim, may afford me more length. Most mini controllers are not meant for arranger application it seems, with split keyboard applications, and I need to know if USB will work like a din plug connection to the SD40. My needs are pretty simple, in that I control everything from the SD40 very easily. I will check this out.

Bernie

It appears that the SD40 is not class compliant like a computer, but I have a Kenton Midi USB Host that should allow me use a USB cable to the it, and regular midi connection to SD40.
UPDATE
I hooked up my M-Audio 61 to the Kenton Midi Host via USB set to global ch 1 and works like a charm.

I have an M-Audio 61 in the box if anyone wants it. Pay shipping.

How much for the m-audio Don? Also, is this the keystation version? PHow about the software that comes with it?

I decided on the Korg Minikey Air 61 from Sweetwater. At 5.5 X 33 in, I can place it under my SD40 and still have room for my other gear.

Thanks to Chris for the suggestion

Too late the M-Audio has already been spoken for! It will soon be on the way to Florida to reunite with the SD40.
I have a brand new Ketron foot controller though. $100. plus shipping. I just paid $149. plus shipping for it. Used it three or four times.

Bernie,
The SD40 has three USB hosts for MIDI as well the USB device port for PC connection. The three USB hosts are indeed class-compliant. If your M-Audio 61 is class-compliant, it should work right out of the box with the SD40. My SD40 recognizes the Korg Microkey Air by name and plays right away. So you don't even need to involve your Kenton USB midi host. Since the Korg Air is also MIDI over Bluetooth, it can even be wireless by using a little Bluetooth MIDI receiver plugged into the SD40.

Chris

My M-Audio is a number of years old, but worked perfectly with the SD40 without any setup except plug it in.
I didn't program any other commands though, but there is software that can be downloaded to do that.

Bernie: You can use a standard USB midi cable out of the Korg and plug the flat end of the USB cable into one of the 3 standard USB ports on the side of the sd40. Should work fine.
JM
Sorry for the replication of replies, since Torch already covered this.