It doesn’t plug in to the processor in the way a G12 should but I’m using that IR repeater with my 861 successfully. Powered off a USB on the back of the TV just now. The 861 IR sensitivity seems a lot less than the G68 they replaced. I believe newer ones had a more sensitive receiver but replacement for the older (v4 and older IIRC) needed the whole display board replaced. This works well for me.

Main system; 861v8 ID41, DSP8000SEU fronts with DSP5500 centre and DSP7000 rears (all in lovely silver) 504, HD621
Second system 861v4 ID40 LPS, G98DH, 504, HD621, 2x DSP5200 with DSP5200 centre
MD600 tucked away in study. Lots of other Meridian!