Picked up a lovely sounding Gate Audio pre from Lawrence recently, in use in the study with a Garrard 401, Trichord Genesis, Pass Aleph M clone and a pair of Tannoy DC6es - really nice.

But it has a funny connector on the back - seemingly connected to the outputs - just wonder what it is?

My guess is either 1) earth socket - looks like it might take a banana plug? or 2) some kind of subwoofer output socket of a kind I've not seen before?

I had hoped to use split RCA cables to run a sub from the mono'd output of the only stereo pair of RCA outs, but it gave me a round loop so I gave up.

Anyway, could anyone enlighten me, I've shown a bigger picture of the overall layout in case that helps.