Ok, it didn't go as smoothly as I hoped for...
I ended up getting Delock ExpressCard to PCIe adapter.
First I tried it in two PCIe x1 slots, but Multiface II / HDSPe card wasn't recognized at all. I checked BIOS settings, didn't find anything relevant, and PCIe power savings are disabled in Windows 7.
Then I moved the adapter to one of those big PCIe x16 slots, and the HDSPe card was found!
I managed to install drivers, but after reboot it didn't work, Device Manager saying that "This device cannot find enough free resources that it can use. (Code 12)"
After another reboot it worked fine again! After yet another reboot it fails etc etc... (No pattern, seems to be random.)
My situation is pretty much identical to this case, except that in my machine the RME Hammerfall DSP is located under sound devices in Device Manager.
I'm afraid that this might have something to do with the chip set, but maybe I should test this with another ExpressCard->PCIe adapter...?
Any other tips that I could try, anyone?
Edit - Here's the setup:
Intel Core i5 3570K 3.4 GHz LGA1155
Asus P8Z77-V LK Intel Z77 LGA1155
G.Skill RipjawsX DDR3 1600 Mhz 16GB (2 x 8GB) (running 1333 MHz, working with that)
CZ Vertex 3 MAX IOPS 120GB SSD SATA III
Windows 7 Home Premium 64bit
(Note: I'm using the integrated GPU)