I was able to get the IR communication all working, so now I'm really close to having basic laser tag functionality. It turned out that my big problem was that I had fried the infrared receiver I was trying to use, and once I replaced that, I was quickly able to get it to work.

As for the sound, I've tried writing a simple program to emulate the I2S-like LSBJ protocol used by the PT8211 DAC, but I still can't get any sound except for a whine from the electrical noise. At this point, I've basically given up on audio for the Genesis gun, and I'll use an MCU with I2S support for the Magnum gun.