Iam wondering it I can use an x-9 med cage with triple rings in front?
With SRAM you can. The chain will be long though in the granny and the higher cogs on the cass. (12-15)
You have to setup the chain like this:
Run the chain around the largest cog and chain ring and add 1 complete link.
If it is on a Full suspension bike you need to have the bike at full travel as well. (if the design creates chain growth)