I emailed Mazda in the My Mazda website about the fitment of CX-9/Speed6 rotors and calipers so hopefully I will get a reply soon.Shared componentry is quite common. I am very interested in this as well. Considering the Mazda parts bin costs are affordable and design is less complicated (coming/compared from German VW/Audi ownership)..for my part, I'll do some digging of my own on part # cross references, between these two Mazdas.
Hopefully, someone else more knowledgeable can chime in on this as well..some confirmation.
FYI, the Sport and Touring CX-9s has 18s rims...adequate enough space for these bigger 12.9/12.8 rotors to fit and work their magic (Grand Touring has 20 inchers).