The ROG MAXIMUS IX FORMULA MB supports up to 64GB and up to 4133MHz OC ram however you should consider also the CPU which officially supports DDR4-2133/2400MHz RAM.
I recommend you choose a kit that have been tested to work with your MB at a frequency supported by the CPU that have been tested and listed on the MB QVL and that way, they will work.
Choosing OC ram very often requires Bios Tweaking if your confident to change RAM Timings in Bios.