Quickly skimming, I see no mention of comms. Ideally, left and right needed to be connected comms wise to integrate their functionality otherwise they act as two independent speakers.

The 5200's have 5 pin DIN sockets or BNC connectors. Initially the speakers will have been shipped with M(aster) and S(lave) cables which were audio and comms combined. You want slave cable, DIN out on master and DIN in on slave. Alternatively, a BNC cable will do the same for comms only, but is not so common.

Meridian owner since 1992
Prime & PSU, Focal Elear headphones, Roon (ROCK 8Gi5 NUC), Explorer 1 & 2, F80. 200/203, various Sonos (via Roon).