Let's see... If I'm willing to do some channel-specific rework for specific instruments, I think this might be salvageable.
The LeCroy scopes are 1V into high-Z output. So if I remove the 50 ohm terminations and replace the attenuators with passthroughs, I'll have un-attenuated high-Z directly to the comparator, and I already know 1V with an 850 mV threshold will work.
The PicoVNA and Siglent SSG pulse trigger outputs, and I think the PicoScope, are 3.3V into high-Z. I should be able to do the same thing there (the comparator can take a 3.3V input).
Then for the Siglent SSG (and future function generator) which have 5V TTL outputs, keep the attenuating stage, but the 5V signal will have enough swing to trip the comparator.
So in short, for all of the input channels that do not need 5V tolerance, remove R53, R77, R89, and replace R65 with a 0R, at which point I have roughly 1-3.3V usable input range high-Z inputs.