You have the answer with Aesthetix Rhea or Io. They have already provided a thoughtful solution built into these units. (unfortunately not in the Aesthetix owners manual) Contact Glenn at Aesthetix and he has a complete solution.
Essentially, you need to run a single signal wire off the (internally bridged, single coil course) the Miyajima Zero, to the #1 input of the Rhea, followed by a dual single-ended RCA cable from #1output on the Rhea. Hence you have avoided the ground loop with the use of one cable containing one +/- source on the input. Also you have given yourself a dual mono output to send to your stereo preamp. Simple and perfect. 1 = mono.
Essentially, you need to run a single signal wire off the (internally bridged, single coil course) the Miyajima Zero, to the #1 input of the Rhea, followed by a dual single-ended RCA cable from #1output on the Rhea. Hence you have avoided the ground loop with the use of one cable containing one +/- source on the input. Also you have given yourself a dual mono output to send to your stereo preamp. Simple and perfect. 1 = mono.