How much software is 7.1? It would not be the first time that M have not supported a format because it is a minority product - think DTS ES and 6.1.

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