A.
anwered by: canteau
A 6000 bearing measures 10x26x8mm and a 6803 bearing measures 17x26x5mm, so the 2 bearings are not compatible.
Depending on the X9 hub version the hub uses (1) 6803 and (1) 6000
The size of each bearing will be printed on the dust shield of the bearing and a complete rundown of all the bearing sizes for all the versions of the X9 can be found here:
https://sram-cdn-pull-zone-gsdesign.netdna-ssl.com/cdn/farfuture/ifiGGtNp5SsOavZxWqJkWVKoS_4TzdmrAoomnJ8cNAY/mtime:1434644542/sites/default/files/techdocs/2016_sram_spc_reva.pdf