Hi Bryan,

> A couple things: I've been using headphones with the mixer,

My guess is that this is what has probably caused the problem - almost
certainly it is not designed to drive such a load, and I suspect the
chip would run pretty hot if you did so, and it has probably just given
up the ghost. If you have any soldering skills, it would be quite
simple to replace the chip to find out, and much cheaper than a new
module!

Tim