For HD output you must use the STB decoding.
For RF or composite the TV does the decoding.
There is essentially only the first caption service.
With that said, I use it all the time. For example, I like solid yellow foreground, black edge, transparent background, proportional w/o serifs, standard size. One 722 works most all the time. The second 722 will drop CC, typically with multiple streams or with much activity (button pushing). On it I can usually get CC back with a skip back or two. It is like the sound dropping on the same 722, which can be cured by changing channels and back or like the CC, just a skip back. The ultimate method to regain CC is to do a soft reset but it sure wastes a lot of time.
TVs do not have as many options and the HDMI and component signal do not include the codes.
-Ken