just to elaborate... summing and mixing is the same thing so you don't need to use the two terms together.
This happens a lot in language so its no biggie:
Torpenhow Hill, is a place in England but its name a derived by the languages of the cultures that lived around it at various points through history ie. "Tor" is SW-English for hill, "Pen" is Celtic for "Head", "hōh" means "spur of high ground" in Anglo-Saxon and "Hill" means "Hill" (obviously) so Torpenhow Hill means "Hill Hill Hill Hill" in various dialects.
no idea about the Aux problem tho!!
i'd guess that to do it all passively would be awkward because adjusting Aux levels would probably alter other things in the system too, but i don't see a problem with putting a very high input impedence active stage onto the channel to drive the Auxes.
...but i'm only new so i could be wrong. i'm sure somebody cleverer than me will be along to help soon.