Tried this last night at the gig, it works. Couple of things I noticed:
1. I dug out two optical cables, not being sure if either were completely functional (don't use them often), I thought I'd try and use them both. The octopre data states that when doing 44.1 or 48 the two ADAT outs are mirrored. So, I had one cable from each output on the octopre ran into the HD24 ADAT inputs 9-16 and 17-24. Adjusted the input map on the HD24 to be digital in for those banks of channels. I was only able to receive signal on 9-16 nothing on 17-24. Swapped inputs on the back of the HD24 and had signal on 17-24 but not 9-16. So, not sure if this is an octopre or HD24 issue.
2. The digital in signals where hotter than the analog signals by about 3db or so (eyeballing it in samplitude). So the octopre digital out must run hotter than the TRS out.