I have an old test PC where I recently installed Windows 10 Pro 64-bit to check the performance and compatibility with devices and applications. The onboard sound card is a Realtek AC'97 which as described in this thread will cause a BSOD if you try to install the latest Realtek drivers. The solution was to manually install an older version of the Windows XP 64-bit driver. Since the driver is meant for Windows XP 64-bit, as you may guess is not 100% compatible with Windows 10 64-bit. It installed the playback devices (Realtek AC'97 audio Speakers and Realtek AC'97 Digital Output) and I can play any sound perfectly, but it didn't install any recording device, so I cannot record any sound.
I have an old Creative SoundBlaster Live! 1024 PCI card (model CT4832), so I decided to install it and give it a try. For each attempt I restarted in Test mode (Disable driver signatures) just to make sure the driver will install whether is signed or not. The official Creative BETA driver for Windows XP 64-bit installed "successfully", but no sound was produced from the speakers! There was no official driver for Vista 64-bit or newer (not even for Vista 32-bit or newer), so I tried the SB_Live_SupportPack_2_5 (unofficial SB driver by Daniel_K). The same again, it installed "successfully" but no sound came from the speakers.
I wasn't so happy that I couldn't use a Creative driver (either official or unofficial), so I got my last resort, the third-party KX Project audio driver. It installed "successfully" but again I could not hear any sound from the speakers (connected to the green speaker output which normally is for the front speakers). I opened the KX mixer and tried to test the speakers, when I got an error that "Failure to produce sound"
I was about to give up when I opened the Playback devices and I noticed 5 devices instead of 2 (Speakers and Digital). These were strangely named "Master Mixer", "Wave Out 2/3", "Wave Out 4/5", "Wave Out 6/7", "SPDIF/AC3 output". So I kept my speakers connected to the green output (front) and then right-clicked on each device and selected "Test". Finally I was able to hear sound from "Wave Out 4/5" device, so set that default. I can perfectly play any sound now. I haven't tested recording from "Recording Mixer" device yet, but I hope it works.
EDIT: I just noticed a setting "Swap front and back speakers" in KX mixer. It was enabled (swap). When I disabled it, the sound now comes as expected from the "Master Mixer" and "Wave Out 2/3". So I set "Master Mixer" default as it should. I think that's one step forward. I'll let you know if recording works once I get the chance to test it. Just for the record, the KX mixer still gives an error "Failure to produce sound" when testing the speakers, but I don't care if sound works in all other applications.
So it is possible to make an old Creative SoundBlaster card work in Windows 10, even on Windows 10 64-bit, but I'm not very satisfied with the way it is done. I would prefer using Creative drivers for best performance/compatibility. Anyway I'll live with that.
PS: The KX Project is available for Mac OS X, for all of you wanting to use a Creative SoundBlaster (and Audigy) card in a Hanckitosh (regular PC running Mac OS X)