Does Khoros community support sign in/ sign up features that are on the same page where a user wants to comment, instead of taking them away from the article they want to comment on or putting sign up / sign in in a pop-up?
Something like this wireframe, with sign in/ sign up beneath comments?
You can change your settings to allow anonymous users to post before they have registered or signed in.
Personally I prefer to make registration as quick as easy as possible and then encourage the user to post. I would hate for a brand new user to spend a lot of time composing a message then lose all their hard work on the message because of an issue on registering.
Hope that helps,