Do you have a source for drivers or documentation? It is using a xilinx fpga chip, no a normal sound card chipset. Is there a breakout cable that comes with it? If not, you will want the documentation to be able to make a breakout cable.

Depends on what you mean by regular sound card. AFAIK this is a card designed for audio workstations used for music production, broadcast, post production editing and whatnot. It is a professional card and not designed for Windows gaming, so it would perform badly or not at all in this task.

If this card is anything like other DAW interface cards I have worked with, it will not have any analog signaling on board.
The Sub-D connection is probably clock sync not MIDI or an analog breakout port. The optical ports are most likely a multi channel ADAT port. If you are lucky the optical ports may be AES/ABU which is somewhat compatable with S/PDIF.

According to the documentation for the card, the optical jacks are S/PDIF and there should be drivers somewhere for 95/95/NT4 that support DirectSound. So it's possible to use as a sound card.

https://www.marian.de/files/marc2p/m2phbus.pdf

Since you don't have the analog breakout cable, you will have to use an optical decoder on the S/PDIF output to get an analog signal.

Well I stand corrected, this card may actually be used as a windows sound card with an external DAC.

Windows drivers appear to be here:
https://www.marian.de/files/marc2/

It looks like there is a standard and pro version of the drivers, the PCB looks like the pro version

https://www.marian.de/files/marc2p/