So I did the composite mode on my 7800 and everything worked,  but was curious about the 6.8k resistor used to balance volume between Pokey and TIA output.   I opted to remove the R5 and R6 resistors and bridge the bottom solder points as well as inline a 6.8k resistor and all is fine, but after looking at the schematics I noticed something intersting.   Appears the stock resistor in R5 is already a 6.8k (which I removed) and the stock resistor in R6 is a 18K (also removed).