That's one way to do it, of course, but it would mean that I'd have to ditch my ADI-8 Pro (which is connected to the Multiface II) and still be left with the same 16 analog inputs (although with 2 preamps this time).
I guess I should have done my research better before purchasing the Fireface 400. For some reason I was under the impression that I would have access to both units i/o channels via ASIO drivers - correct me if I'm wrong, but isn't this the case with, for example, when two Multifaces are connected to the same computer?

I did a quick research into different RME manuals, and it seems that you can do the same with multiple Firefaces. Is it always limited to the same devices (i.e., two Fireface 400's or two Fireface 800's, 802'sm UC's etc...) but not with, for example, Fireface 400 + Fireface UC/UCX?

Anyway, it seems that the most sensible (but pricey) way to solve my problem is:

1. Buy another Multiface II + OctaMic (or some other A/D with preamps & ADAT connections) and sell the Fireface 400.
2. Sell both Multiface II & Fireface 400 and buy a Fireface 802 instead (it's got 2 ADAT connections, so I could even buy anohter ADI-8 and be able to use all 30 channels via ASIO driver)

A "cheaper" option 1 could be, that I'll keep the Fireface 400 and use it in standalone mode - instead of buying an OctaMic (or alike). But, at least for me, it feels kind of silly to use a full-featured audio interface as a simple A/D converter...

Regards,
Pekka Nissinen

It all depends on how often you need all inputs (and/or outputs). If allays you need a better solution, but if only rarely  and for recording only, you could create a recording setup with asio4all. It will not be the best latency (the default 512 seems to work best, but I tried it only briefly in a distant past) but it will be easy to switch once set up.

You will need a computer with HDSP card to set up the Multiface and then keep it powered on. No way around it.