room acoustics

I'm tearing out the panelled walls in my listening room and have the opportunity to design some acoustic treatment into the room as I refinish it. My reason for posting is to seek advice from those who have travelled this path before. The only plan I have so far is to make the amplifier/speaker wall absorptive (via several inches of insulation). I'm most concerned about the effects of the sliding-glass door and the off-center fireplace. A description of the room follows. The room is 12 by 19 feet. (speakers are on the short wall.) The leftmost 3/4 of the opposite wall is a brick fireplace. (the other quarter is the entrance to the kitchen ... no door) The left wall also contains a sliding glass door. The right wall is uninterrupted until you reach the rear of the room, where there is another passageway ... 90-degrees to the aforementioned Speakers are full-range, and the listening position will be out in the middle of the room. Any help is appreciated. David