The control signal is proprietory, without the ability turn them on, select a source, they are likely to be as useful audio wise as a cat scratching post.

However, all(?) other Meridian DSP speakers also have a serial protocol for home automation. For later SpeakerLink speakers, this is part of the SpeakerLink connection - a dealer should be able to supply a simple cable converter. If, and it's a big if, the M6 supports this, then it's a simple serial text protocol that any terminal emulator or bit of code can interface with.

So a SPDIF + RS232 to speakerlink connected to suitable source and control unit *may* do what you want.

Alternatively, a cheap legacy multi media controller or processor, such a 562v2/3 or 568.1/.2 plus a SpeakerLink dongle such as Reviver or homebrew will do at low risk as if it doesn't work out you are unlikely to lose much cash on resale.

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