The Verizon FIOS setups that I have, use a variant of the Motorola DCT6200 tuner, which will work out of the box with the DCT6412 template that is in our database.
In LinuxMCE, you have two choices of how to handle TV watching: (1) you can either use MythTV for TV viewing and recording, or (2) you can simply treat the cable box as an AV device in the system, and have LinuxMCE handle switching and controlling the device. Ironically, I opt for option 2, because MythTV simply does not lend itself well to live TV watching when bolted to an external cable box (the latency between channel changes is noticeable, and can drive some people crazy).
Currently, I have the device controlled via a USB-UIRT, which is connected to my Amplifier (which is an Ethernet controlled Denon 2312CI), Once you've added the cable box, either via Sarah, or via the web admin, you should see scenarios which will allow you to select the cable box, and use it, causing the TV to switch.
The 6200's still have component outputs, which can be passed through a Hauppauge HD-PVR (the original 1212 unit), to distribute the signal to other media directors, and to allow Orbiter's UI to be laid over the top. The newer DCT3200 tuners, however, only have HDMI, and currently there is not an HDMI capture device that will work correctly under Linux for this particular application, at this time.