A recent post about DMC waveform output put me up to the challenge. I don't have a NES development system to try it on real hardware, so I'd love to find out if it works (perhaps with minor adjustments). I wrote a short web page with illustrations, asm demo code and mp3s of its output when running on an NSF player that handles DMC interrupts:

http://www.slack.net/~ant/nes-emu/dmc_waves.html