IT'S ALIVE!
(If the thread title means nothing to you: This is an Arduino-based player for old Nintendo video game music.)
And here it is: Hardware Nintendo NES VGM player with Arduino: Demo and explanation - YouTube
Lots of work still to do, but I figured I'd share in the meantime, as these things tend to take me forever to finish. 
Short technical explanation (the video covers this in greater detail): I'm using an Arduino Mega to communicate with a Ricoh RP2A03G via an 8kb dual-port SRAM. The RP2A03G (hereinafter referred to as the "2A03") is the custom 6502 CPU used in the North American version of the Nintendo Entertainment System. It also contains the audio hardware, which is accessible to the 6502 core through internally-mapped IO ports. Writing to these from the Arduino is done by proxy: A small 6502 program is written to the SRAM by the Arduino before the 2A03 is brought out of reset. Once the 2A03 is up and running that code, the Arduino can send over addresses and data and affect writes to anywhere in the 2A03's address space.
More as the project evolves!