giuliomoro Thank you so much for the thorough answer.
I think you've answered my question but to clarify, by AUX I just mean an external audio signal going into the adc. My idea is kind of a reverb fx loop with processing happening on both sides of the spring. An external audio signal goes into the left channel, gets processed in pure data and drives the spring with the left speaker out. Then, the spring returns through the right input channel, is processed again and output through the right channel. The goal is to only use built in amplifiers on the bela, both to drive and pickup the spring reverb tank.
The speaker outputs and headphone outputs are the same stereo channels and cannot have separate signals routed to them, right?