Well, after using "chuck --probe" and determining what card has what number from ChucK's perspective you can start chuck with
chuck --dac3 --channels6
myfile.ckhere the "3" would represent the number of the soundcard to use and the 6 the number of channels you'd like to use (this would be both in and out, see "chuck --help" for more options).
Once you have that running you can ask for a certain channel from your soundcard's input in your code using "adc.chan(4) => my_ugen", where the "4" would hopefully be the right channel. Remember we start counting at 0 yet the labeling on your hardware likely starts at 1.