Thanks for the reply!
The issue I'm having lies with Logic's default routing when creating summing stacks. It looks like if the tracks are all routed to an aux already, creating a summing stack will use that aux as the summing track using the bus that is already assigned. If no aux exists, Logic will use a new bus.
In my template, I have all my music tracks routed to an aux using bus 64. If I want to create a summing stack for my strings, for example (to process them together), Logic will use bus 64 to send the strings to the summing stack track, replacing the music aux I already had in place.
So it looks like in my case, I'll need to keep doing what I was doing in Logic 9, and just manually route the tracks to a bus and route the newly created aux to my music aux. I can then use a folder stack for organizing, if necessary