Made some more progress in reverse engineering the Pinnacle PCTV HD Pro Stick. I broke out an oscilloscope and with the help of the publicly available datasheets for the CX25843, CS5340, and someone kind enough to tell me where the reset pin was on the xc5000, I traced out a bunch of the GPIOs for the various components. Still some more analysis to do, but I'm making progress.
Wow, my eyes don't work as well as they used to. Even with my magnifying visor, I still had trouble tracing out the PCB. I think I've still got one of those benchmount magnifier/light contraptions in my father's basement. I should see if it's still there...
Updated the wiki page with the GPIO and i2c findings from the last couple of nights' work:
I still haven't tracked down why the xc5000 didn't respond to i2c commands after loading the firmware. Will have to see if I can figure that out tomorrow.