I think I know what you are asking...
Sounds like you would need to do stereo sends for your AUX outputs. Your headphone amplifiers would need to support stereo (2-channel per headphone output). Basically, just pan everything to either side at the input and then route those inputs to your your AUX outs. If you are looking for individual mixes to send to an AUX, you may want to try using a Matrix instead of an AUX. The Matrix sends usually provide better options.