Problem solved.

I followed this great article : https://n2rac.com/dmr-digital-amateur-radio-setup-several-instances-dvswitch-server-3694caaf6bf1

Then : 

# cp /opt/Web_Proxy/ /opt/Web_Proxy2/ -r

# cp /lib/systemd/system/webproxy.service /lib/systemd/system/webproxy2.service

# nano /opt/Analog_Bridge2/Analog_Bridge.ini
and change the following : 
[GENERAL]
pcmPort = 2223
    
# nano /lib/systemd/system/webproxy2.service
and change the following :  
WorkingDirectory=/opt/Web_Proxy2
ExecStart=/usr/bin/node /opt/Web_Proxy2/proxy.js 8081 2223
    

# nano /opt/Web_Proxy2/proxy.js
and change the following :   
var wsPort = 8081,
    pcmPort = 2223;

# systemctl enable webproxy2
# systemctl start webproxy2
# systemctl status webproxy2  

Τhe above procedure ensures that RX-Monitor audio for the second instance will be independent from first instance.
Then
# cp /var/www/html/index.php /var/www/html/index2.php
#cp /var/www/html/include/browserdetect.php /var/www/html/include/browserdetect2.php
#cp /var/www/html/include/config.php /var/www/html/include/config2.php
#cp /var/www/html/include/config.php /var/www/html/include/config2.php
#cp /var/www/html/include/functions.php /var/www/html/include/functions2.php
#cp /var/www/html/include/lh.php /var/www/html/include/lh2.php
#cp /var/www/html/include/localtx.php /var/www/html/include/localtx2.php
#cp /var/www/html/include/status.php /var/www/html/include/status2.php
#cp /var/www/html/include/system.php /var/www/html/include/system2.php
#cp /var/www/html/include/tools.php /var/www/html/include/tools2.php

And edit recursively all "version 2" .php files (starting from index2.php) to point at second instance's locations and also all .php files references to "version 2" .php
I believe you got the point.
Second Dashboard is accessible as http://<IP-Address>/index2.php