I had the ADA8000 and now have the ADA8200 which has way better pre-amps, in fact i still doubt of they are even better than the UR816C’s.
But I mostly still use my Yamaha N12 for recordings and external pre-amps.
I wil further do some tests with your explanation mentioned and come back with results.
I am very pleased with the UR816 as my second interface, mostly for outboard gear connections, but as you say, the routing is not that easy and poorly explaned in the manual.
And thanks for joining the UR816C world on this forum, pratical users advice is always welcome.