Alright folks,
I have found a workaround.
First, as I described before, I'm using Realtek High Definition Audio as default and first sound device.
I opened the engine_config.txt to investigate the problem and set the sound device.
engine_config.txt file is located at [...]\Documents\Mount and Blade II Bannerlord\Configs\engine_config.txt
These are the parameters we focus:
disable_sound = 0
sound_device = 0
When I launch the game with Realtek High Definition Audio the game change these parameters to:
disable_sound = 1
sound_device = 3
(the lists in programming start at 0 not at 1 so the device selected here is the 4th)
I forgot to say in my first message that to display the list when launching the .native.exe I added a headset in an other output. But first I had only 3 sound devices. So that the sound_device = 3 point on no device. But when I added a headset the there were 4 devices so that the list displayed in the game option with the last Item of my sound device list: BenQ.
When I was changing sound device to other device than the first one there were no sound because of the disable_sound = 1.
The workaround is to use another output than my first output: Speakers (Realtek High Definition Audio) RTKVHD64.sys, version 6.00.0001.8470
So now I use BenQ set as default in my system. I set manually the parameters to:
disable_sound = 0
sound_device = 0
engine_config.txt file is located at [...]\Documents\Mount and Blade II Bannerlord\Configs\engine_config.txt
This do not solve the problem that I can't use my real sound device wich is in surround.
For all who have sound problem I hope that it may help you.
Farewell.