wakethetown - Please read my email again; digest the email, then read it again. The REL sub GND (black wire) is not connected (floating) according to S3/SHO manual (page 13); unless you have the REL/PSA resistor network connected. If you have bought that network and have a BHK amp, the REL GND (black wire) gets connected to the BHK250 (-) post. I connected my L/R REL GND to the bottom (-) and RED & YEL to the bottom (+). If you read my last sentence, you are connecting 500 ohms from the BHK250 (-) posts’ to the BHK250 chassis GND. There would be no need for the REL/PSA resistor network if the solution was to connect the REL GND (black) wire directly to BHK250 chassis GND. This is not electrical engineering, it is logical. This REL/PSA solution provides the PSA BHK balanced differential amplifier (-) output a reference to chassis GND through a 500 ohm resistor. When the AMP is in standby the PSA BHK amp output is open allowing the REL GND (black wire) a path to the PSA BHK chassis GND, preventing the “hum” heard when the AMP is in standby.
Also, in REL’s defense, there are a lot of amplifier configurations: class A/B, D, non balanced, balanced, mono, stereo… As a designer I have seen situations where I thought I covered all the customers configurations to find out I missed one.
I hope this helps,