rs-750lcd

Doesn' t the RS750 have a designated alarm disarm wire or does it share the same wire ? You might be able to by installing the Momentary to Constant Output relay diagram here ( Momentary to Constant Output ). The only problem as you know is that the driver's priority door lock is only pulsed but the factory alarm disarm needs a  constant (-) current during the entire remote start sequence or the OEM horn goes off. Try this diagram and see if it will work. On the screen it looks like it will work.

Another thing I just though of...wouldn't you need to hit two buttons everytime you want to emote start the vehicle if you have it set up this way ? First you have to manually disarm the OEM alarm by pressing the unlock once and then you can remote start the vehicle, am I not correct ?

Actually you just program the unit for which feature you are using.  If you program for drivers priority unlock, it just pulses upon the first press of the unlock button, and if you program it for disarm, it pulses before remote start automatically and also upon unlock. 

I didn't think you needed a constant negative for disarm.

Basically I think i would need to find another wire that will pulse before remote start, and also upon unlock if I want to use both.  Otherwise i will lose drivers priority unlock. Kind of stupid if you ask me.