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/message/10363#10363 Note that all Arris boxes are made by Motorola.
Come back if it that doesn't help either.
I have a Slingbox M1 which I use in Puerto Rico (Liberty Cable with HD service). Cable box is Arris DCX-525e. Slingbox functions properly but cannot find cable box, and consequently remote for functionality. Any suggestions? Remote supplied by Liberty is UR5U-9020L-LI.