We are still happily using our legacy system, with the Motorola DCX3400 being the box that has worked best for us. The previous box was a Motorola RNG200N, which we didn't care for and Xfinity was able to find us the current box.
Our box has a very slight fan noise, and I was hoping to swap it out for the exact same box. I called and was told my local store had several of the boxes I was looking for. What I ended up picking up was the RNG200N, which had a horrible noise (very loud steady buzzing). Needless to say, I hooked my DCX3400 back up.
If there is a Xfinity emploiyee that could help me track down the DCX3400, that would be appreciated. At some point we will probably move to X1, but for the time being, we would like to find this exact box.