I went to my local comcast in Skokie IL and got what seems to be a new Motorola DCX3400 box. I don't have the "M" version, I think that is only for people who pay to get the service in all rooms and they told me a technician has to come out to install that one. The box I have is black and large. My old boxes were all thinner and silver, also this remote is a darker grey color instead of bright silver. It seems to have a 320 hard drive. I don't recall what my older models were, either DCH or DCT...I think they were DCT. Hope this helps.
you are the mercy of your local comast office when it comes to boxes. The newest if the multiroomdvr box, you might be able to get this seperately if your lucky. Most of the newer boxes in the last 5-6 years have hdmi