The Yamaha MGP16X (17.59” x 19.48” x 5.62" / 447mm x 143mm x 495mm) is a fit for the Gator G-TOUR-GRC12X12. The only measurement of concern is the height of the mixer. The mixer is 5.62”/143mm tall and the top wedge of the GRC will accommodate up to 115mm. There is also 80mm of clearance above the rack. See below.
If you have 80mm of clearance for "straight down" gear (assuming there is only so many mm you can exceed the top wedge depth before it contacts the back of the rack case) and the combined total clearance for gear is 115mm + 80mm (195mm total), then subtract the gear depth (195mm - 143mm), that leaves you with 52mm/2-inches.