This question comes from awolch:
“Do the analog inputs on the GPIO accept modular levels or do they only accept 3.3v as on the original board?”
CV is only safe through the four primary TRS jacks and their associated test points. Normal GPIO pins have the usual limits established by the processor, usually 0-3.3V. Some pins are actually 5V tolerant. See the processor datasheet to be absolutely sure (edit: I will add this voltage tolerance information to the testpoint pinout part of the documentation). Inputs to the processor
ADC need to be scaled and limited to respect these limits.
+12 and -12 rails are available for expansions though. Creating an expansion that could safely drive the processor
ADC channels with CV is theoretically possible. Another approach would be to use a separate multichannel high voltage codec on the expansion.