Hi Elle, your articles are fantastic. I think I worked through some of the same tests you did while exploring 36-light spectral mixing. I wrote a separate post here https://discuss.pixls.us/t/spectral-rendering-scene-linear-ocio-etc/5715
I have only implemented Normal mode and a mode called Weighted Geometric Mean, which is very similar to multiply. The results are very interesting when you go from RGB (3) to 36 spectral wavelengths. Cheers!