I couldn't find how to do this anywhere on this forum so I figured I'd post it anyways. If you'd like to use an old remote (Grey with red OK button) to control your new X1 cable box (Mine is make Arris model mx011anm) follow these steps:
1) Hold the SETUP button until the indicator light blinks two times.
2) Enter 9 - 8 - 2. The indicator light will blink four times.
This unlocks your remote.
3) Hold the SETUP button until the indicator light blinks two times.
4) Enter the code 01982
This should make your old grey remote (That can control your TV, AV Receiver, and Cable Box) work with your new X1 receiver. The reason this is important to me is because the provided XR2 version U2 remote can only control your box and your TV. You do lose a little functionality with the old remote when interfacing with your X1 box compared to the provided remote but I feel the trade off is worth it for me.
I discovered all of this via Comcast's online chat feature with a tech support representative.
any help would be greatly appriciated as you cannot use two voice remotes on the same box.
It would be neat to be able to do when two people are watching.