Room acoustics with wall placement

Hello folks,
I have a question for those with experience in acoustics and room elements. I'm revisiting a small media room configuration in a finished attic. Aside from an overhaul of some of the components in the room, I'm looking to add a wall to hang a plasma display, but am concerned about how the room acoustics will be effected. The wall will also afford me the ability to place a center channel below the TV, rather than where it is now (similar positioning, but 3 door cabinet supports a TV with the center channel inside of the cabinet).

How far forward should the speakers be from the wall, and will the addition of it impact any low frequencies?

Thanks in advance.

Thank you for your responses and for the advice regarding the room orientation and acoustic treatments. Admittedly, the current positioning is far less than ideal. I have intentions of modifying the orientation in the long term, following a partial dormer. In the interim, I'm forced to make do with the current orientation based on the size of our furniture, and the frequency of which I entertain guests in that space to during certain sports events.

Thanks again.