I have found that you can’t gang channels of a different sort together. for example I have set up a mix output as a Post-Fade Aux mix to use for stereo Subs rather than the system provided MONO sub chennel that still takes 2 mix channels 
and I noticed that I can’t gang the mix and the sub masters together.
I we have the mains ganged anyway so I now have 2 faders L & Sub instead of L & R.
We use matrices for the FOH fed outputs too which is nice.
Duncan Whitcombe
Mirror Sounds & metrochurch
Perth, Australia
T112, iDR48x2, Dante soon
http://www.mirrorsounds.com.au
http://www.metrochurch.org.au
