using multiple sets of speakers in stereo configuration (for movies)

I have hit a wall while trying to configure my stereo setup in my apartment. i'm trying to always take my stereo/audio setup to the full capabilities all the time, and i'm one small caveat away from making this idea work. hopefully someone can help me figure out this workaround.

i have my mac mini 2011 desktop setup to the right of the doorway (audio goes out FW800 to a pro tools mbox and outputs to the speakers), and there's a home stereo receiver to the left. the receiver plays to those shelf speakers, as well as speakers around the corner in the kitchen. both systems work well independently of each other, and sound like sets of speakers when they play sounds.

current situation: i finally ordered the long 1/8" extension cable to plug my mac mini headphones port into the stereo receiver, connecting the two. primarily so that i could switch outputs in system preferences and play tunes from my computer in the kitchen while cooking, but i learned about Aggregate devices and Multi-Output devices and i was able to use both systems at the same time, too.

but while i was ordering a 50' headphone cable extension, i got a long AC power cable and dvi as well so that the lady and i can put my monitor on the coffee table, connect it up, and sit on the couch to watch a movie with some popcorn n all that. the lady is pleased with a movie and popcorn, but i am unhappy with the options for getting the movie to sound right. We're watching pretty much in the sweet spot between the two systems.. here's my options:

1) __LR or LR__ - play the sound from either individual set of speakers. lady is happy, i can't stand it.

2) LRLR - play each system in a stereo configuration, lady is still happy, but it's still phase inconsistent. i am unsatisfied.

3 LLRR - this is the holy grail.

inside of the Audio Midi Setup window, i created a multi-output device called FULL STEREO to use the mbox and the headphone output @ the same time, and tried to "configure speakers"

i want my mbox to play the right channel through both speakers, and the built in output to play the left channel on it's two speaks. but it's not an option. check the error message.

I am hoping to not have to get out the soldering iron to make this work, but i am thinking i may need to get a small mixer and make some custom cables! i wanted to come and ask for advice first. can anyone help?