I'm under the impression this, at least for now, will only be possible by either:
a) Using 8 channels of ADAT or AES, plus 16 channels of USB
b) Using 24 channels of MADI, DANTE or AVB with one of those expansion cards. That is, of course, when they are available.
c) I may be a litle confused here, but the manual suggests ADAT and AES 1-8 cannot be used at the same time? Have I got this wrong? To get 24 channels without USB or one of the expansion cards, it would take ADAT 1-8, AES 1-8 and ANALOG 1-8.
Since I mentioned the expansion cards, I would very much want a Thunderbolt card, compatible with TB1, 2 and 3; Preferably Thru-compatible, so it can be used in a chain.
I don't think (a) will be very straightforward, and you'd end up with potentially different latencies between the USB channels and the ADAT/AES ones. You'd need to use an aggregate device, which are sometimes problematic. If you wanted the outputs to go somewhere other than your computer, then this wouldn't work.
(b) is certainly a good option. MADI and Dante expansion cards are currently in beta test so we expect them to be available soon. AVB isn't currently planned.
(c) There is a limitation that prevents us from using all channels of ADAT and AES at the same time. This solution would also suffer from some of the same problems as (a), in that the latencies would be different between the analog and digital paths.
We are planning to develop a 32 channel Thunderbolt card. We've had quite a few requests for it so it will probably be the next one we make, after we release Dante and MADI.