I ended up making a box with outer dimensions to fit the Kallax width, and order custom rails for the inner diameter of the box. But, as you might see from the picture, I failed to take into account that the screws would add width. I think this will barely work with "sink in screws".
I don't think I will bother to rack my Mother & Subharmonicon. But start from here for now. The main goal for this rack was to able to play around, tactically / hands-on / no computer. The Grandmother sits on top. Now all I have to do is actually make som music with it.
In this patch I run the Mother through the Spring reverb of the Grandmother and mixes it in. I feel that this is a bit lacking, and will probably add an fx module next. Possibly something simple like the Disting or PicoDSP. My guess is that this case is slightly "underpowered" I have to keep that in mind as well (6U/2000ma).