That's a lot!
Compared to its siblings, the Mini only has a quarter of the Ram and half the processing power. I understand Linkplay groups use a primary/secondary model where the primary device in a group takes on the role of receiving the stream and then distributes that to the secondary. Consequently, it might mean a Pro or Plus would have to take on that primary role.
I think your use case is probably fairly unique so you would really need WiiM engineers to say definitively what could be achieved. Contact them by email or by raising a ticket thru the settings/feedback section in the WiiM app. Good luck.