btw, here are photos of the prototype. It easily fits on a Busboard BR1. The only part that is not available as a thru-hole part is the flash memory chip, which needs an adapter. So if you want to build one but are put off by having to make a PCB for it, this is the simple solution (provided you can read a schematic and know how to solder).

Wiring is done with wire-wrapping wire. I have some pre-cut lengths that I bought as a package around 1980 (!) - still haven't used them all up. But you can just get a spool and cut them to custom lengths...

The two empty sockets are for testing the DAC as an audio output. It's easy to generate triangle waves. Passed through a low-pass filter, they don't sound horrible.