Today, I found a solution that solves the 75% of the problem.
FIRST OF ALL
install a virtual interface like MOBIOLA (I used it, to use my iPhone4 as Webcam) ... install the Windows version if you have it or MacOS version ... it's up to you ...
Here below I continue with Windows, since I'm not (yet) a Mac User
The italic notes, are explaining the reasons of each setting
MOBIOLA is downloadable from here (09 Feb 2018):
http://mobiola.com/
WINDOWS SIDE
1. Control Panel > Sounds > Communication: select "DO NOTHING" and click "OK"
This avoids that Windows dims or mute any other audio source, when Skype is activated
SKYPE SIDE
1. Tools > Options ... > Audio Settings
2. Microphone: select your Audioboard -
The audio out of your card, sends the signal to SkyPe
3. Speaker: select Mobiola -
The audio out of SkyPe is sent to this driver and not to the Audio Out
4. Video Settings: select OBS-Camera -
OBS will send the Video Program to SkyPe
OBS STUDIO
1. Tools > Virtual Cam > Start -
you can close the small popup. OBS send the Program to SkyPe and to the streaming server
2. SOURCE: + > Audio Input Capture > select MOBIOLA, click OK -
It receives the audio from SkyPe
3. SOURCE: + > Window Capture: -
You select the area where SkyPe correspondant appears
START THE STREAMING!
At this point, on Facebook or Youtube, the audio you send, is broadcast, and the interviewed person, is seen and listened.
She can listen to you very well by your microphone.
People can listen to her, via her microphone
WHAT IS YET MISSING?
I didn't find any way to send the audio FROM OBS Studio (Program Audio) TO SKYPE.
I did try to send the audio to MOBIOLA,
Settings > Audio > Desktop Audio Device: select MOBIOLA
On the audio source:
Right click on the cogwheel of the Desktop Audio track > properties ... select the audio interface out
Nothing happes ... useless action
