There is no "Xfinity button" on either the box or their remotes. What box are you refering to here? Anywho, regarding the Arris RNG150N. The Motorola RNG150N manual is about 99% accurate to the Arris model. Menu access is as follows: From the remote, power off the box then immediately press the menu button. The settings menu should launch where you can force the HDMI mode, how it handles 4:3 programming, video and audio quality and other things.
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