I can't answer your question directly, but may be able to point you in the right direction.
First, have you been able to find the correct code for the Samsung TV and map it to the soft "TV" button the top of the 8300 remote? If so you will definitely have control of at least TV power, volume, and mute. If not, go to the Cablevision Customer self-help webpage and search for the code and method to map control of your TV to the 8300. Hopefully this will get the remote "talking" to the TV set.
Note there are several versions of 8300 software in use (SARA, Passport, and lately Navigator). I don't know which your local Cablevision headend uses, but some of them support the ""Video Source" button (grey, lower left corner) functionality for TV source select. If it works, it will probably just cycle through each possible input in a loop, so it will be a bit more ciumbersome than "direct source" select that the Samsung remote offers, but that's better than nothing. I think the Samsung allows you to block out any unused inputs which should speed the process up a bit.
Second there is a wealth of info buried in the AVS forums (but finding the answer you need may be tedious). Below is a link to the HD recorder page. In it is a very long thread, over 8000 posts, that for example covers use of the 8300 in a SARA environment on a TWC headend. There may be a similar one for Cablevision, or there may be some gems in that one that will apply to your situation:http://www.avsforum.com/avs-vb/forumdisplay.php?f=42
Finally, you might consider getting one of the better third party multi-function remotes from Harmony, Logitek, or similar. Many of them can easily be set up to control all the functions of all your theater devices, and probably group them into logical "macros" too. This will make it easier for you and others in your household to "run" the system.
Hope that gives you some ideas!