Hi John,
I don't have HW running right in front of me and being so am not using the proper terminology per HW either, but I think all you have to do is include your Aux / mix down channel(s) in the 'send' section under the general settings / audio tab. As an example, if channels 1 / 2 are set up for routing the great manual division and you want 5 / 6 to also receive this signal, include 5 / 6 in the send to channels section. Keep in mind to do it properly, in this example 5 / 6 can not be designated as use for pipe / rank routing. I also believe without looking at my own set-up that you can not create a separate 'mix' group and make it do what you want it do, so you would need to delete the mix group and again just assign whatever channels you want the mix to go to. Under general settings / audio there's a split screen, you will see something worded like primary use for pipe routing, those are your audio groups for pipe / rank routing, directly under that you will see the send to's, they should be blank, use the pull down in the sends to find the channel you want the channels to send to and select those channels and you should be good to go. In this case you would want each of your divisions to 'send' to whichever channel(s) (the same channel) it is you are using for mix down.
I hope that helps,
Marc