It's been a while since I updated the thread. Well, thanks to luckybob, I discovered such thing as slot exhaust fan 😀 No, seriously, I never knew they existed.
I tested Crystal 4236 in Descent 3, Dethkarz and Turok 2. As long as volume is not set high in Windows and "Crystal 3D" is off, the sound is pretty good. I need nothing more.
So I went on and removed Aureal Vortex to make space for two slot exhaust fans:

In order to make better use of the hole where floppy drive should have been, I mounted a low-profile FAN I had lying around. With extra rubber padding. To my surprise, it turned out to be very quiet.

The PCI card fixing mechanism turned out to be no good for fans, so I replaced it with spare ATX chassis:


This is what I had as a result:


The issue I had before stopped at the cost of some extra noise and no A3D. I have only 2.0 speakers, so the second thing does not bother me much.
Considering XR385, I switched to software S-XG70, which proved to sound just as good. I was unable to spot any actual difference in FFVII, perhaps with a slower CPU it gives a performance hit, but PII-450 is way over FFVII system requirments.