I have an SD40, and the only reason I didn't buy the SD90 is because it was more than I needed. I take my SD40 to many engagements. including my Karaoke show and with my Hammond SK1. Also, as I get older, less weight is more of a factor.
As an aside, I am happy Curt is spending so much time and effort to teach us more about these amazing modules.
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pa4X 76 ,SX900, Audya 76,Yamaha S970 , vArranger, Hammond SK1, Ketron SD40, Centerpoint Space Station, Bose compact