Is that possible to set dns on the server (cpanel) to forward some subdomains on one server and another to another server ? like SERVER1: xxxx1.bigboy.com xxxx2.bigboy.com xxxx3.bigboy.com SERVER2: xxxx4.bigboy.com xxxx5.bigboy.com xxxx6.bigboy.com
You will just need to host your subdomains on respective server and then change A records of all subdomains to point to correct server from the DNS zone of your main domain.
I am not sure what exactly you are referring too but you take take an example of DP itself. I believe DP's forum is hosted on different servers then their main web site.