from what i can tell it seems as though youre on the right track. the way it works is you bind keys on the alt accounts to macros then on the the main account when you push the button the multiplexer presses your macro. simple as that. if youve got it replicating keys then thats half the battle. personally i have it replicating all keys except w,a,s,d i keep those for my main only. every other key is fair game you just gotta figure a way to set it up.

currently my keys are set up like this:

2- fires off mages fireballs and lock's shadowbolt
q- is all the lock's DoTs on a cast sequence
3- is shaman heal main or main's friendly target
4- drain soul to make shards
5- earth shock for spell interupt and occasional just-for-fun quick finisher
0- all clone buffs
e- is life tap
t with modifiers- is the shamans totems

at level 26 thats all ive needed so far it will get much more complex. i havent integrated the other spells in yet cause im easily clearing the instances as it is so i decided to keep it simple for now till it just wont cut it anymore.