Well, all of the codes posted by jehill, Lyndell McGee, and me are functionally the same, and any of them would work.  I'm not sure why Lyndell wanted to modify the GI IR protocol or why he thinks it is device 96.  But in reality all of these Pronto Hex are nearly the same, and DecodeIR.dll shows all of them as GI Cable, device 0, function 74/75.

jehill, I do think you are wasting your time.  Roughly speaking, there are more than 20 million of these cable boxes using the General Instruments (since purchased by Motorola) IR protocol.  You're not the first person to have desired and looked for discrete On/Off codes.  However, if you really want to look, there is a better way using your Comcast remote, which is already known to be shooting the correct timing and device information.  Plan on spending a half hour, but you can test all 256 possible IR signals.

The procedure is simple.  Make sure the box is on and the remote is in Cable mode and then tap the Setup button, and enter 00140.  That sould make the channel number increment by one.  If that works, you've got the procedure.   Now systematically go through every number from 00000 to 00255, observing the result after each 5 digit entry.  If you hold the last digit, the IR signal will be sent repeatedly.  

Of course, some of these 5 digit EFCs are already known, so you don't really need to try them.  Here's a list with the first two zeros omitted.