I am just curious, what’s your Sigma Foveon workflow?
I got a cheap 2nd hand Sigma SD Quattro, it became my favorite camera now.
Seems none of the FOSS does X3F RAWs. So what you do?
I shot always RAW+JPG. JPG is only used to see in Windows what the image is about. Next step is load the folder into the Sigma Photo software (SSP) - there I do nothing and save the images as 16bit TIFF (usual size ~130Mb). And then process with darktable.
Please let me know if you are Foveon shooter!