The Synchron series is not set up for MIR the way the Studio series is. In Studio the Synchron Player has a "MIR unprocessed" mixing preset. Select it, then route to MIR and you're good to go. The Synchron series have no way that I know of to turn off the baked-in mix. You can adjust it, but you can't remove it.
So if your goal is MIR, go with Studio series.
W 10 i5-9600K 64 GB
Synch - Woods, Brass, Perc I, Str Pro, Elt Str, Dua Str & Sordino, Prime
Studio - Woods, Perc, Solo Str, Ch Str, Orch Str, App Str, Harps, Choir
St Dim - Brass, Strings
VE Pro, MIR Pro 3D, Vienna Suite Pro
Cubase 14, St One 6, Dorico 5