I've been able to use the usb on my X-station to get the audio from my synth into pure data via adc~

I can also use the 1/8" jack on the side of my macbook as an audio input.

I want to know if it is possible to run both of these inputs at the same time. I know you can do multiple midi devices in the input menu, but I don't remember if there was an option for multiple audio ins.

I've never done it, but there is a Use Multiple Devices button in the audio settings window.

on OS X, create an "aggregate device" somehow (I don't know the details, I never used OS X, just remember hearing about it).

on Linux, you can do the same with ALSA, but it requires intensive hacking on config files to get it to work.

in general it's a tricky problem, because different audio devices will have slightly different clocks, so one might be 44100.01 Hz and the other 44099.99 Hz, and they might even drift slightly over time relative to each other, so keeping them in sync is a hard challenge, which is why pro-audio adc/dac often have separate clock sync inputs