Sounds like you want a 'stamp your feet' thread lol. Believe me, I'd've used it a lot the last wee while in work! As for the 'shout out' do you mean a bit like facebook when you can 'like' a post/ comment? Something like that would be good.
Sound off is just posting a message. People aren't supposed to talk back to it because then you are taking away that person's right to say how he/she feels and also, this would generate an argument which is never the purpose of it. You can say whatever you want and say, "this is my sound off". And messages are tend to be in general. True definition is something like, speak one's opinion without fear or hesitation and/or express complaints, discontent, displeasure, or unhappiness etc.
Shout out is more like a twitter kind of thing. You can say, let's say for example, @ ----, you have to kiss a lot of frogs before you find your prince charming. (lolol)
Or you can express a message directed to your loved one – could be your girlfriend/boyfriend, husbands/wives, pet animals, actors etc. Could be anything, really. We have a newspaper that does it and it really is very funny and sometimes very heart warming. Can be tasteless at times too. lol