I've had 2 different fully balanced amps that I wanted to connect my Rel sub to. 1) Ayre V3 - I called the tech support guys. They told me to connect the ground wire to one of the scews on the chassis. I did and it worked great. 2) PS Audio HCA-2 I sent a request on their tech support forum and was told by Paul McGowan who responded to the post to install a 1Kohm resistor in line with the black wire and the negative speaker terminal (I had tried the Ayre chassis screw trick and it did not work).
Not sure if this info is useful to you, but do know that if your amps are fully balanced don't connect the ground wire to the negative speaker post whatever you do.
If they're not fully balanced and you're only concerned about a ground connection to the preamp, one option is to fabricate a ground strap chassis to chassis.
Not sure if this info is useful to you, but do know that if your amps are fully balanced don't connect the ground wire to the negative speaker post whatever you do.
If they're not fully balanced and you're only concerned about a ground connection to the preamp, one option is to fabricate a ground strap chassis to chassis.