It appears like you are trying to reinvent the wheel. Personally I'd abandon any attempt at doing this. The only and main reason why I say that is the fact that you can connect the properly tagged wires from one unit to the other all day long and it may be correct, but the simple fact that the communication protocols between the 2 units may not be compatible. Its like one japanese man taking to the chinese man, It may sound similar to an outside observer, but they still need a translator to properly communicate.
IMHO, it may be a lot of work, with little payoff. But if you do get it to work, I will be the first to give you props.