Well, the short version is that v1.3 works perfectly.
The new boost converter doesn't seem to have any trouble powering the game, at least with fresh batteries. Some testing with reduced voltage is pending to see how far that goes.
The audio crosstalk is gone, now that the DAC line doesn't go near any of the LED rastering lines.
I've made a couple of small improvements and now ordered a 1.3.1 board. That likely will go into the Tindie store once it's arrived and verified.
So... now there's nothing to do but get on with the case design.
Speaking of that, the speaker shelf is a failure, unfortunately. The threaded inserts don't fit. I'll have to iterate that design and try again.
Well, there are some things that need validation.
The system operates normally down to 2.3 volts, then loud audio makes it unreliable. The question there is whether that's acceptable or not. Hopefully it is.
The other issue is that the soft power system is unreliable. When off, there's enough leakage to make the LEDs turn red. The soft power MOSFET gate is something like 2.mumble volts even with a 1kΩ pulll-up resistor. Clearly something has to be done about that.