I think that this project and the overall spirit of this forum are great! Nothing like sharing experience and expertise.... building on the backs of others' work.
A small point of note: On the audio board, it looks as if the labeling of the op amp sections is incorrect. Op amps A&D are on top (pins 1,2,3,12,13,14), while C&D are on the bottom (pins 5,6,7,8,9,10). Also, FWIW, for somewhat better performance, perhaps it might be worth looking into using quads (LM324) for CV, and duals for the audio stages. I used dual high performance op amps in my A/DA build (which I adapted to a quad DIP).