would canreinvite be recommeded as it allows rtp to bypass trixbox server thereby reducing cpu on server

I wouldn't recommend it. It is only useful if there is no NAT between your phones. EG: It helps reduce load if you have a public trixbox server and public phone on the call together. Because there needs to be a direct connection between the phone behind the trixbox server and the person making the call. If you have your trixbox NAT'ted then turning canreinvite=yes on will most likely cause a ton of problems for you. That is why we leave it off by default in trixbox.