Sounds like you guys have done a ton of work to get towards a working peachy-clone printer using whatever could be salvaged from the fallout of the project. I have hopes of eventually building my own Peachy now after reading through some of your accomplishments. Mostly posting here to keep track of the thread, but being a professional software developer and Arduino programmer myself, if there's any assistance I can offer, please please let me know.

Couple questions, I know initially the Peachy was supposed to run off of common sound cards, that was scrapped because everyone's hardware was different. In the meantime the Raspberry Pi Zero W has arrived on the market, and it is a known quantity when it comes to it's audio circuit. Could something be built around the audio-out on that board, or it's GPIO as it's far more capable than the older Arduino chips. An ESP8266 might also be an option, could be code-compatible with what's out there, and is bit faster. Plus Wifi!

Anyways just my $.02 and hope of eventually having a Peachy-type printer of my own some day.