Have you been to http://wdtprs.com/blog/ or http://www.newliturgicalmovement.org/ ? But as for a forum? Sorry, can't help much. Maybe one doesn't exist? But people here do like to talk about anything liturgical-related, and occasionally theological...(but those sorts of discussions can get exciting quickly...)
I second that, Marajoy. You could certainly start liturgical discussions here in the general discussion category. I don't know about anyone else, but for me, I'm half music man, and half Master of Ceremonies (at our cathedral, btw, so there's plenty of action!). I won't speak for anyone else, but I always enjoy chiming in on a good liturgical discussion.
And since you specifically requested a forum similar to this one, you can't get much better than staying right here! :)
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