Is this something that can be altered via Lua scripting?
I have a growing number of songs that use MIDI out on select instruments to drive external events (mainly graphic applications). I work on the songs on different machines, and the names of available MIDI out devices on each machine are different. I got tired of manually setting these instrument settings so I wrote a tool for myself. You can read about it here: http://neurogami.com/blog/neurogami-loading-custom-code-in-renoise-tools.html
The basic idea is the tool looks for a custom folder holding a Lua file named after the currently loaded song. If that file s found it gets loaded; the file is expected to define a function that sets song properties using Lua.
I have it set to simply add a tool menu item so I can manually trigger the code, but it can just as easily be coded to automatically invoke the code.
If you can follow my write-up and do a bit of Lua scripting you could create for yourself a tool that automatically updates the audio out properties, assuming this is something that can be done using Lua and the Renoise API.
If you want to do this for every song then you can skip the code that checks the loaded song name and just invoke code on the opening of every song.
https://forum.renoise.com/t/adding-song-notifiers-on-song-load/39402