You have server groups, set the permission in that which will apply through the whole server. The Admin would be in the Server Admin group, and everyone else by default will be in the guest group. You can of course modify that. Just for all your server groups set push to talk and also the 'skip' option for that permission. That will make sure it's always applied....I won't bother explaining how it all works, it's quite complicated, but trust me, I have one of the most complicated permissions set on my server, and I know how it all works.
Channel permissions only apply while they are in that channel, the server groups apply through the entire server. Channel Groups apply only within that channel (can change between channels). Individual permissions apply through the entire server to only 1 person.
Hope that helps some.