For those techies that want to dabble in advanced audio signal digital filtering and processing, digitizing, playback, using low cost microprocessors, …
http://www.pjrc.com/teensy/td_libs_Audio.html
Uses Teensy 3 which is a superb 32 bit ARM Cortex M4 with an Arduino compatible set of libraries, plus advanced ones such as the above.
Sparkfun sells some Teensy products; there are several, with Teensy 3.1 being the latest. https://www.sparkfun.com/products/12646
There are also some piggyback boards for it, for Ethernet, SD cards, and the like. Again, Sparkfun may sell some of these too.
(disclaimer: I have no vested interest in the manufacturer.)