Hi,
For my Mongoloti synth I thought it'd be cool to have an internal speaker Volca style to make it more portable. Is there a way to get audio out of it without affecting the main audio outputs? Can audio be directed to an analog pin? I could then output it from my Teensy.
P.S. Yes, this is scope creep. 
The audio can't be redirected, you'd have to tap in with a wire for the left and right outputs (IC4 pin 16 and 5, I'd think). Since you'd need an amplifier anyway, make sure its input is high impedance, possibly using a buffer stage before the speaker driving amplifier, then it will not affect the outputs to any significant degree.
The solder holes behind the jacks serve this purpose: R=ring, T=tip S=sleeve, three groups of "RTS" for the three corresponding connectors.
I don't understand. Are you saying you want to be able to direct some stuff to the internal speaker and some stuff to the line out?
Because if you just want the internal speaker and the line out to be simple duplicates then it makes sense to do this in the analogue domain as suggested by DrJustice and johannes. The way you're talking about sending it through GPIO sounds like you want separately addressed mixes though?
Another trick you could do: connect your internal amplifier to the switched tip&ring points of the line out connector. Plugging in a cable into line out will then mute your internal amplifier...
That's a good idea. Does the axoloti already have switching jacks that aren't doing anything?
Yes, all jacks including the headphone out are switching types, and the switches are unconnected.
Is this the synth where you are using 3 axoloti boards?
I have no idea what's possible but am curious as to what can be done with chaining boards. Is it not possible to back route the final mix to the output of axo 1 or axo 2 for an internal speaker?
Thanks all. Using the headers behind the line out is a good idea. When I said split, basically I mean when line out isn't connected the audio comes out my internal speaker. Connecting a jack to line out cuts off internal speaker and it goes out to my mixer as normal.