I assume you have already done a proper Forum Search for your model number in case other people have already answered your question ?
If so and that didn't help then check out this thread: https://community.sling.com/thread/3300?tstart=0
Come back if it that doesn't help either.
(NOT a Sling Media representative, just another user)
I recently acquire Xfinity X1 as well and my android phone Slingbox player remote control did not function the way it was supposed to. So, what i did, i went to the my Slingbox account website and reconfigured my setting when looking for the cable box top, i typed comcast and used the "X1" cable box model, finished the setup and it worked!!!! yay!
Good luck. Hope this helps.