Win9x is much easier than DOS:

So long as the two cards don't have the same resources, you just have two sound devices in Windows and can choose whichever one you want.

If one is PnP and the other isn't, make sure to reserve all resources used by the non-PnP card as "Legacy" in BIOS.

And how do I do it if both of the cards are PnP and they use the same resources? I'd like to use my AWE 64 Gold and Turtle Beach Tropez Plus in one system.

Cards with PnP can negotiate over what resources they use. It's the whole point.

But the device manager just shows me a bunch of yellow symbols if I have both cards plugged in. So what does that mean?

Just to be clear does each card install and work fine by itself?

By itself they both work perfectly. I also tried installing windows with only one card plugged in, installing the drivers and then afterwards plugging in the second card and installing its drivers. The second one is all shown with yellow symbols and the first one is not being initialized properly.

Try different PCI slot combinations. What is this bios option set to: PNP OS Installed?

And PnP works in theory. Some cards may just get along no matter what.

They are both ISA cards and I do only have 2 ISA slots 😀 PNP OS is set, yes.
No other ideas?

Are you able to manually change resources in device manager?

I was able to change one of the devices listed resources after disabeling all parallel and com ports. However for instance for the joystick port I cannot chose any other resources.

Then disable the joystick port on the other one if possible, you should only need one.