I have always hated the distance between my boards with a double setup. After a dozen or so over the years,I finally found these:

https://www.quiklok.com/product/qlx-3-second-tier-add-on/

The base is adjustable,fitting over most tube diameters. I use this on my On-Stage X stand. The hight is adjustable to just clearing the bottom keyboard,or two higher.
I wish I could attach it on my table stand.
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pa4X 76 ,SX900, Audya 76,Yamaha S970 , vArranger, Hammond SK1, Ketron SD40, Centerpoint Space Station, Bose compact