Thank you spinaltap but I've just noticed that the BNC comms cable on the 8K is connected to the output stage of the master speaker and is connected to the 808 by SL. I wonder if that is why it is not accepting commands from the 861 as that unit does not have an SL connection.

If I attached the BNC to input, I wonder if that would solve the issue? I'm loathe to swap the comms around and FU.

DSP8000USE, DSP5200HC, DSP33, DSW1500, 808v5, 861v4, WiiM Pro+, Panasonic 55" Plasma, DMP-BDT700 Blu-ray,
MECOOL MEon1, Russ Andrews Signature Power Block, UltraFuses, SuperFuses, Kimber Signature PS Interfaces.
Prior: DSP7000.2, DSP6000.2, DSP5000.2, DSP5000.2HC, 508.24, 568.2, 596, G98DH & G68D.
Jaguar F-Type; Meridian 770W Surround System