You'll have to make some stereo compromises but you can treat each channel of each stereo output as a separate output. If you have theee stereo pairs of outputs, then you have six mono outputs (think of them as A, B C, etc).
To assign a channel to an output, assign its stereo output to the lair that contains your desired output, then pan the channel left or right. If you want output E, for example, assign the channel to stereo output 3 and pan it left.