This is the first time I contribute in this community forum... glad is to help instead of asking for help, which I will need shortly
I'm quite new to Axoloti, but experienced in audio engineer stuff, lately I've been studying the Axoloti board to build an enclosure, and like you stumbled in some doubts regarding pinout wiring.
For what I can understand, the PCB pins marked with L IN+, L IN- and R IN+, R IN-, will allow a stereo "balanced" audio input in Axoloti. Using L OUT+- and R OUT+- will allow a stereo "balanced" audio output.
The two jacks that Axoloti has from "factory" are stereo in and out, but unbalanced, since each of the connectors uses one TRS JACK for L and R. I guess to save space and costs.
For the audio Jack soldering, you must use the following:
-TIP: Will use the pin marked with + (plus)
-RING: Will use the pin marked with - (minus)
-Sleeve: Goes to GND
I checked with a Multi-meter and found no connection between Jacks in the board, and the prototyping pins, that puzzles me. Not sure if they are isolated for some reason, or you can actually access more in/outs this way...
Hopefully somebody can shine some light here.
Well I hope this info it's of some help for you!