Have you tried memtest86 on that machine, or any other types of stability tests?

My old 486 used to lock up in SVGA very easily. It was basically unusable.
It would also lock up in 320x200 VGA, but less easily. If only a portion of the screen was animated, like looking through the windshield of a car racing game, it was pretty stable. As soon as I'd switch to an external view, animating the whole screen, it would soon lock up.
If I had QEMM running at the time, it would give an error message. The late DOS games that used DOS/4GW would also give an error message when they crashed.
This problem was only resolved when we upgraded to a new motherboard. Our 486 board was unstable, and the intensity of graphical activity definitely corresponded to how crash prone it was. I believe that the volume of data traffic was influencing it's stability.

I removed Trio64V+ and with the integrated Cirrus Logic everything works just fine, including SVGA. No freezing. With Trio I didn't have any refresh rate problems, everything looked really good and Windows 3.11 support was better but I guess I'll have to settle to the integrated one. I do wonder though what was the cause.

Does your Trio64V+ have socketed RAM chips? I wonder if corrosion on the pins could cause this kind of problem.

Well, if you had Windows 98 you could look in Device Manager to see the
Resources that each Audio setup uses (when each audio device is setup
with the other audio device out of the system). Maybe the Trio64V+ can
be set to use alternate settings, same as what Cirrus Logic uses, instead.