I've thought this for a while - on the basis that the Youtube and Forum are pretty essiential, and serve slightly different purposes, maybe there is a case for disabling the Wordpress comments and just directing people to Youtube for general comments and the forum for more detailed discussion?
The advantage with Wordpress comments is that you don't have the sign up for anything. So it caters for the signup-phobic members. And then you wouldn't be able to reply to someone Youtube comment there if you disabled them.
I don't generally get a huge number on Wordpress anyway, and I don't want to take anyway anyone outlet for comments generally.
Alternatively I wonder if there would be a way to have a comments box on the Wordpress that just pushed comments through to Youtube somehow?
I don't think that's possible, as you need a Youtube account to do it, so there would be no transparent of who wrote it.
At least with the Youtube --> Wordpress direction, you get a link to the persona Youtube username and channel.
Youtube probably won't like it either I suspect.
Dave.