S/Pdif will work…but don't expect the best clock sync from it.
Routing is actually available for the H8000Fw. Check the Eventide website, H8000Fw page> Software Updates.
Yes, AES 188 thru 18 are the ones wired thru the DB25.
I don't know where exactly the SRC is applied but I would think it's before the DSP so that it's not taking resources away from FX.
The question about analog and aes is a bit vague as routings need to be considered in relation to DSPs I/Os. If you want a DSP coming out of analog and the other out of AES-EBU, you can. The concept is about configuring MAIN inputs and outputs first. You will always have 8 of them and you need to decide which type og protocols they use, as there are a few dozens I/Os. The Routing flexibility is very open, with a few limitations described in the manual.