Here's a used "Reference" MC for $375.
https://www.usedcable.com/synergistic-research-reference-ac-master-coupler-x-series-active-15-amp-ie...
Not sure what the difference is between it and the standard MC.
https://www.usedcable.com/synergistic-research-reference-ac-master-coupler-x-series-active-15-amp-ie...
Not sure what the difference is between it and the standard MC.