Donny
I think you need to think of your needs, first module or SD9, second, will you use the advanced features of the SD 90 or SD9 to the extent of the price difference to the SD40,eg. I am an absolute dumb cluck at midi. I, even had no problem except when I tried something out of the ordinary, but I am very content with a basic midi setup, and don't try and send midi control messages to parameters that are right in front of me on the touch screen.
SD90- a fine flagship, but I didn't need that modern stuff. For you, it is self contained with more controls on the board so you wouldn't have to reach up and touch the module(no advantage to me). The advanced features, for you, may, or may not be fully utilized.
SD90 and SK1, or any other controller, would make it more versatile, and not confined to one keyboard.
To summarize; I looked at the very same scenario and loved the Hammond sound, as well as Ketron styles and voices, especially, with AJ's basic package, which adds so much more to an already large palette of sounds and styles.
The last factor, for me, was the use of a small Korg Microkey Air and my SD40 at six or seven pounds total-under my arm and out the door, and what a sound.
Everyone is different-just my take
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pa4X 76 ,SX900, Audya 76,Yamaha S970 , vArranger, Hammond SK1, Ketron SD40, Centerpoint Space Station, Bose compact