Welcome & congratulations on your purchase! π
The official approach to using MIR is indeed to add a separate instance to each individual player. In this way, MIR can unfold its "magic" with rich spatial envelopment and beautiful coherence (a.k.a the "glue") between all the instruments.
However, it is also possible to use MIR for an ensemble of instruments, regardless of whether it's an actual recorded signal of a section (e.g. "1st Violins") or just a submix of individual players (e.g. "Cello 1 - 6") that's routed to a shared bus/group channel. Just make sure that the input submix makes use of the full L/R stereo width, as MIR is meant to take care of all panning tasks. Pre-panned signals, i.e. signals with a "baked-in" bias towards one side, reduce MIR's ability to create a convincing spatial impression within a mix.
These sections of MIR 3D's and legacy MIR Pro's manuals will help, too, to make the most of your recent investment:
-> https://www.vsl.info/en/manuals/mir-pro-3d/getting-that-sound
-> https://www.vsl.info/en/manuals/mir-pro/hints
... if you are completely new to the world of MIR 3D, it might be helpful in general to take a look at the manual to avoid a few typical traps and misunderstandings. π And please don't miss the tutorials available in MIR's sub-section of VSL's web site:
-> https://www.vsl.co.at/en/Vienna_Software_Package/MIR_Pro_3D#!Video_Demos
-> https://www.vsl.co.at/en/Vienna_Software_Package/MIR_Pro_3D#!3D_Setup
Enjoy MIR 3D! π