Hello!
I can configure CP-8961 for use with FreePBX. But not exavtly us you want.
And I can't configure CP-8831. And I think nobody can.
CP-8961 needs Asterisk with special video-patch. So, I can install additional Asterisk - it will be as additional call-leg (may be just on the same computer with FreePBX) to be as a proxy between CP-8961 and FreePBX.
Except that, I need admin acces to your dhcp/bootp server.
And most understandable for me - how to turn off / turn on the phone remotely and see what is's showing on his screen remotely. If you can suppose methods for it - themn I can try to resolve your task.
For example, you can install webacm what will be shot screen and translate video to internet.
But what to do with power-off / power-on?...
So, what do you think about all of this?