First, let me just say hello and an early thank you to anyone who takes the time to respond. I have been a long time reader of this forum but this is my first post. I'll apologize for the length of this post up front, but I figure it's better to get as much detail in as possible.
Anyway, so at the beginning of this year, I finally got the thumbs-up to do a front-projection and dedicated home-theater room in my basement. As you'll see in the pictures, I designed the room completely without acoustics in mind, and as a result, I'm now going back to the table again for the next step; making it sound better.
Currently, the sound seems too bright to me. Additionally, I get OK bass when I use my subwoofer (Axiom EP500), but I don't get good bass at all from my front mains which have a reputation for putting out very good bass (Axiom M80 v2).
My goal here is not to worry about soundproofing as much as sound-deadening to present the most accurate tonal response and best possible soundstage/imaging. I'm working with a fairly narrow room so I'm willing to do whatever it takes to get that soundstage to spread beyond those side walls (if possible)
The room itself is roughly 11x20, but the back wall opens up to the rest of the basement (see pics). The foundation is concrete and the theater room has a low-profile carpet (not plush, maybe 1/4" thick I'm guessing). The rest of this half of the basement is just tiled lenoleum directly over the concrete.
The walls are standard drywall with aluminum studs and as far as I know, non-insulated (the basement was finished before I bought the house)
The couches in the theater section are microfiber and fairly fluffy. There is absolutely nothing soft in the entire back half of the basement and nothing on the walls in the back half either.
The ceiling is a bit strange. It is a drywall ceiling, but because there is a beam running the length of the house, they drywalled around the beam, creating an uneven ceiling surface in this room. As you can see in the picture, there is a drop of 6" about 65% of the way from the left side wall. The height of the ceiling is 7' 4" in the high part and about 6' 10" in the lower part.
There is also an odd cutout on the right side-wall of the theater where it too, drops in about 6" to go around a beam (this is also visible in the picture).
The Media-Shelves (Book cases) along the right wall are going away which is going to fully expose this wall.
Despite the big screen, I listen to about 95% music (Stereo) and 5% movies so my main goal here is to improve the stereo music soundstage/imaging and the best possible mid-range and bass.
Also, I only sit about 7' away from the front speakers when I listen so I am definitely in a nearfield listening configuration.
So this brings me to my set of questions:
1. I'm willing to scrap the framed movie posters hanging on the left side wall to replace with panels if the general opinion is that it will make a big difference. Question is, would I benefit from panels on these side walls even with those big couches there?
2. Given my odd ceiling, what would be the best way to reduce reflections up there? Is the uneven surface potentially causing issues or excessive reflections? Does the fact that it's a fairly low ceiling make me even more susceptible to bad reflections?
3. Would I benefit by putting thick curtains up that go across the entire front of the room (in front of the screen when not watching movies and just listening to music)? Is that screen causing any issues?
4. I also considered putting a thick curtain across the back of the room (at the back of the couch) to semi-isolate the theater room from the rest of the basement. Would having that curtain there work any wonders given the fact that there is a very reflective back half of the basement? Or does the fact that I'm sitting so close to the speakers in the front nullify what's going on 12 feet behind me?
5. Given that my current carpet is a low-profile (1/4") on top of cement, would there be any noticeable benefit to upgrading it to a thicker, more plush carpet? Or, would placing a large 8x10 area rug up in the front area where I sit help at all? Or is the low-profile carpet on the floor doing about as much as a carpet is going to do?
6. My A/V equipment shelves are right up front near the speakers (about 4-5 feet away). Is having them there affecting the sound in anyway? Causing any reflections or "livening" the sound at all?
And finally, any general recommendations and advice would be GREATLY appreciated. If you see somthing in the pictures that sparks an idea, by all means...throw it out there. I want to make this sound amazingly accurate and I know that at this point, the acoustics are my biggest obstacle.
Here are the pictures of my room, as well as a Visio drawing of the layout with dimensions.
Visio Diagram of the relevant half of my basement:

From the back of the theater, looking forward to the screen WITHOUT my listening chair in place:

From the back of the theater, looking forward to the screen WITH my listening chair in place:

From the front of the theater (screen to my back) looking toward the back of the basement:

From Behind the back couch, looking to the left of the theater (the other leg of the 'L' that forms this half of the basement)

Thanks again in advance. You guys all seem to really know your stuff and your advice is greatly appreciated.
-Ben