So, a little birds nesting and a lot of fiddling convinced me from moving away from the AD chip with opto-couplers. So, I went for a MAX232 after all, with benefits.
So the setup for the ADMC32x is now:
The other side is this module is more useful as I can use it on other experiments. The other way was too sensitive to bumps and knocks and I need a “quiet” interface because the problem is working out whether I am getting code onto the chip – and not whether my birds nested serial interface is up or not.
10MHz clock is still coming from MAX CPLD.