I am starting to understand how the kind of Ladder DAC used in the amazing Soekris dam1021 works. This article from MSB is a good introduction on the topic. Bottomline: using this design would allow us to replace the ES9018 DAC converters by a bunch of resistors, a few shift registers, and a ton of VHDL code. Bad news: the VHDL part would be hard. Good news: it would be cheaper than using 10 ES9018 devices, and it would simplify clock distribution.
If I can find a similar solution for the ADC part, I’m going for it.