You can setup the tappoint for each aux mix individual, that means that e,g the aux mix for the guitar player is set to post gain, without channel processing, all input signals will be sent to that aux mix without any processing. Anouther aux mix can be set to post EQ, for instance.
If you want to send only particular channels without processing to some aux mixes, you also can assign the same input socket to two channels, one with processing for main mix and aux mixes with processing, the other without any processing for that aux mix which should be fed with the unprocessed signal.