4-channel audio panning?

I found some software to encode audio into dolby digital AC3 files (supposedly, i haven't tested it yet), and i got thinking, suppose i got good at drumming, wouldn't it be neat to mix the tracks into dolby digital 5.1 surround sound. cool, yes? problem is, i have not yet found software to pan the audio around the channels.

now, my analog 8-channel mixer can handle 4 channels of output, sort of. main L/R, and Aux L/R. i can independently pan the aux channels, but the main channels can only be panned left or right, and if i slide the gain fader down, it will fade down what goes to the aux channels too. so if we assume the main channels are connected to front L/R, and the aux channels are connected to surround L/R, then with my mixer, i can pan to the surrounds, but it will always be on the front channels too. besides, my audio interface to my computer is stereo anyway. so surround panning with hardware, short of building a completely new mixer console, is not available.

so, that leaves software panning. i have not found a windows option that is very cheap to free anywhere.

so, both options not available, leaves building something. now this is not a task for the faint-hearted. the LFE, or sub-woofer channel needs only a crossover. the center-front channel can be done independently as well. that leaves 4 channels to pan, preferably with a joystick. fair enough, probably can be done with an Arduino. but the actual act of panning the audio (mono input channel) is where i am stuck.

obviously, i still need a 6-channel recorder, of some sort, but when i/we figure out how to pan the channels, maybe i can figure something out for recording.

the panning portion only needs one digital stereo pot, and one mono digital pot, or maybe just three mono pots (front and rear left to right are controlled at the same time).

I have found a few digital pots, but i am not sure if they can take line level audio.

I found a PT2257 that looks promising, but it isn't a balance pot, just volume. it could work, if i had 4 of them (one for each channel).

has anybody found something else that could work?

thanks in advance for any help.