It certainly works with ADAT and a mix of ins and outs from different converters. I use the output of my mr816x to feed a compressor that goes to the input of a Motu 828mkII.
But them we could discuss if the ping latency should be measured in samples and not ms.
I do parallel compression with this setup, but the compressor has a wet/dry knob, that makes it easy and always in phase. I have heard that the external instruments/fx is on the todo list from a Steinberg employee, but what was around the time Cubase 7 came out. Anyhow with the major popularity of modular synths and the need to feed those with signals I hope what a remake of external instr./fx has moved up the todo list.