If I remember correctly you need to use the .sys equivalent of oakcdrom, vide-cdd etc that came with the sound card's software and not just any driver. That plus mscdex should be enough.
Check the readme files, they often have examples.

This is probably the problem.

I should find a driver that can address mscdex to the sound card (/ P: 376,168)

in the readme and in the installation floppy it speaks exclusively of CDSETUP.SYS which is correctly loaded and started (but is used to associate the port and the irq)

judging by this readme, it should be just as you say ... check it tonight and see what I find!

SOFTWARE PACKAGE CONTENTS

Package 1) DOS/Windows 3.1 installation package:
------------------------------------------------

The 82C931 software package contains (1) 3.5" 1.44M diskette.
- This is the DOS plus Windows 3.1 installation diskette

The Installation diskette has the following subdirectories and
files:

a.) Installation files
- INSTALL.EXE - installation program
- INSTALL.DAT - on-line help text file
- CDROM.CFG - CDROM Config File
- README.TXT - This file
- SOUND16.CFG - Device Configuration File
- LOGO.BMP - Company Logo BMP File

b.) DOS Drivers & Files
- SNDINIT.EXE - SNDINIT2.exe loader
- SNDINIT2.EXE - hardware config and test program in Non
PNP environment
- VOLUME.BAT - DOS volume setup program
- CDSETUP.SYS - CD-ROM setup device driver
- DEMO8.WAV - 8-bit Wave audio file
- DEMO16.WAV - 16-bit Wave audio file
- SOUND16.CFG - Device configuration file
- xxxx.SYS - CD-ROM drivers <<<------------------------

unfortunately my disk does not contain drivers, perhaps because it does not install from dos but only from windows 3.1 and windows 95. i searched the net and apparently the dos version has instead a "drivers.zip" file that it uses during installation .. but unfortunately I can't find any for the 931!

I find a lot of them for 924/925/929/930 but during the installation phase they don't find the card (being a 931) and it doesn't go on.

even those present on vogonsdriver are only for Win31 / 9x ... 😓 the search continues ...

Here's the drivers.zip that contains all the drivers, taken from some card with the 931 chip. It's for all possible devices and interfaces (Sony, Mitsumi, Panasonic, ATAPI...) so you will need to find which is the correct one. Worst case try them all. Normally during installation you select the type of cdrom and it only copies the relevant file from drivers.zip.

Sorry for the delay in replying, I was convinced I had updated the topic!
In the end I found a cd installation floppy with OAKCDROM.SYS updated but at the end of 97 ... it worked great!
I also changed the CD player because unfortunately the Philips 8X did not read me some brands of CDs ... I put one a little more recent.