First, here are a few articles I would refer to every time we come across an issue with changing channels using the Slingbox:
The first two articles deal with the IR (infrared) cables' positioning and troubleshooting. The third article runs you through the process of reconfiguring the virtual remote to match your cable box (In your case, it'll be Comcast X1). Running through these articles should help you identify where the issue is most likely coming from.
As far as the positioning of the IR cables on the X1 box, I would do my best to make sure at least one of the cables is positioned so the bulb is pointed towards the IR sensor on your cable box. Every cable box is different, so I don't know for sure where that is on the X1, but you can always try one position, and then the next, the next, etc. If none of them work, you could be running into an issue with the cables themselves, or you may have the wrong remote configured (refer to the articles above).
Hope this is helpful!
The technology is the same, and the IR sensor is definitely somewhere. When you're ready, I would re-position the IR cables, and try changing channels with your Slingbox. If it doesn't work, try another position. I would make sure the bulb is facing towards the IR sensor (front panel of your cable box), but not actually touching it. Maybe 1-2 inches in front of it. The positioning of the IR cables shouldn't need to be too terribly precise. If you try 3 or 4 positions, and none of them work, I would move on to some more troubleshooting.