Hi Greg,
Yes, you will be able to plug your Xfinity cable box via HDMI and prompts will pop up. If they do not pop up, change your Source to the HDMI port you connected your cable box into, to begin. If you need any help, you can call us at 1-800-SAMSUNG, 8 AM - 12 AM EST, seven days a week.
~Samsung Advisor
~Samsung Advisor