MIUI 9 China Developer ROM for Mi Max 2 can be only flashed through Fastboot method.
For Tutorial on How to install using fastboot method visit: http://en.miui.com/a-234.htmlDownload Link :

http://bigota.d.miui.com/7.8.17/oxygen_images_7.8.17_20170817.0000.00_7.1_cn_4e886698e1.tgz (2125M)