Thanks for the interest and kind words! They make the endless hours spent on the project worthwhile 
Nick, a crystal can't directly produce the needed frequency for the AD725. The chip needs a strong (buffered) clock signal. The AD725 datasheet has a reference schematic for the oscillator, or you can simply use a crystal oscillator like I did, although they are more expensive and maybe harder to find.
Sure I can release the source code. Just give me a few days to clean up the code and add the playback routine. The code is in a pretty messy state because of many optimizations and because I wanted to release the video as soon as possible.
Here's a few things worth mentioning to maybe get you an idea what's going on:
The hardest part was getting sprites to work. I had to painfully cycle count the scanline routine so that it fetches tile data and masks sprites on top of the scanline while outputting a pixel every 6 cycles. After pulling in tile indices from RAM and tile graphics from ROM, there is hardly any time left to do sprites...
Audio is double buffered, so that at the start of each scanline video generation routine pulls a byte from an audio buffer. An assembly routine mixes 4 audio channels and fills up another buffer during vblank. The buffers are swapped at vsync. Timing needs to be precise, otherwise pops and clicks can be heard.
Audio mix + game logic takes around 40 scanlines so it just fits to the vblank period. There is hardly any cycles left during screen refresh.