Maybe a red herring, but what was the +3dB fix for and does it apply here? Was it just DSP's and Direct preset or did it affect anything else?

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