The IR Blaster(s) from your Slingbox should be facing the glossy, slightly transparent section on the front of the Xfinity X1 set-top box. Also, make sure you reconfigure the virtual remote for "Comcast X1". To do this with your Slingbox Solo, go to "Setup.Slingbox.com" on a PC or Mac that is local to the Slingbox (connected to the same network). From Setup.Slingbox.com, click on "Get Started", select your Slingbox Solo from the directory, then click "Configure Inputs". From here, Setup.Slingbox.com should walk you through the rest.
Hope this helps!
Sling Media Forum Moderation Team