I could be wrong, but I think the issue is that the EBMM is an active bass with a lot of output from the onboard preamp and its slamming the Sadowsky. Splitting the coils will reduce the output, think humbucker vs single coils in a guitar, there by reducing how much input is hitting the Sadowsky preamp. See if you decrease the volume from the bass does it decrease the distortion of the Sadowy. I have a similar issue with a Jazz bass I built that has an OBP-3 running at 18V, and I can’t run it into anything I want clean with the preamp switched on.