Gain level on a REL sub

I'm using modded Klipschorns, 103db have only one of the signal cables connected to each of my 300B monoblocks,  REL volume control only two or three clicks up from minimum. Two signal cables connected massively excessive volume. This with two REL TX9 in 13 W x 35L room, diy custom build 6' L sub cables, Speakon connectors single signal wire and ground to each sub and amp, ground wired to chassis screws not negative speaker binding post, bare wires at amp end.

I had this same issue with my Carbon Special. I could not get the high level connection working with the Ayre amplifier I was using. It turned out the problem was that I had the ground cable connected to one of the Ayre’s chassis screws (the foolproof way to connect high-level to a balanced amp according to REL). When I finally tried floating the ground cable (ie connected to nothing), the problem went away and now the sub kicks like a mule on steroids. 
 

Perhaps oddly, I didn’t have that problem with my Yamaha 2100 integrated when connecting the REL’s black lead to the Yamaha’s phono ground. It’s also a fully balanced amp, so not sure what the difference was. 

Another thing, you want that high-level cable cut as short as possible once you finalize your sub placement. It makes a difference. 

Lots of information on REL web site. I also think it’s maybe the wiring?