The MIDIBox Mixer project is free for non profit use only. The hardware and software and any device that incorporates it may not be sold without express written permission from the author. If you want one, you'll have to build it yourself. If you sell this product, you are in violation of this license.
This project uses a modified version of PGA driver code provided by Pilo
Some info for this project was gathered from:
Electronic Projects for Musicians, Craig Anderton
The Art of Electronics, Horowitz and Hill
Building a six channel mixer, Sam Electronic Circuits
The MIDI Technical Fanatics Brainwashing Center, Jeff Glatt
Big thanks to all who helped.