@ Nic: The fronts are greyed out, but the subs aren't, although they are set to DSP & Narrow. I do wonder if this is a problem
@ George: 5/6 is what is shown in the connections page in mconfig & I think it is labelled as side/subs on the 568.

568.2mm, DSP6000, DSP5200HC, DSP33 rears, HD621, LG G3, Sony UBPX800-M2, F80.