Yes, your Slingbox 500 and Slingbox PRO-HD will work with the new Xfinity X1 Platform; however, you will want to invest in an HDMI Adapter/Splitter as these boxes have HDCP (High-Bandwidth Digital Copyright Protection) installed and will shut down the audio and/or video with a base HDMI connection. You can see an example of one of these Splitters on our accessories page:
You can also find these in electronics retailers, but you will want to make sure these are labeled with "HDCP Compliant" or "HDCP Bypass".
I hope this helps!
Sling Media Technical Support