Determining reflection points

Also:
Using the mirror technique where you see the other speaker's tweeter on the side walls.
Where each speaker's tweeter bounces of the rear wall to your ears at listening position

See: http://www.realtraps.com/art_room-setup.htm)

I don't think this will answer all your questions, but the diagrams should answer some.

There's an Acoustic forum over at Audiocircle as I know you frequent there. There's several manufacturers that are very kind and helpful even if you don't buy their products.

Don't forget bass traps. Doing your room acoustics will create a major upgrade that most of us hadn't anticipated and wouldn't do without again.

Just don't over-treat your room.
It's a common mistake.
Start small with 1st reflection points,
then experiment with absorptive/diffusive or both kinds of materials to treat front wall.
Bass traps help with coloration of lover frequencies and will smooth-out a boomy bass in problematic rooms ( I use Echobusters phase 4 for their flexibility. One side is a diffuser and the other is absorber).
In my opinion this would be a good start.
Later you can try treating a back wall.
In my newly constructed room I have used a 1/4inch natural cork tiles to cover entire back wall & few shelves with books as a natural diffusers.
Treating a ceiling is another matter, but not many are willing to go the extra mile.
Email me if you have any specific questions.
I will try to help you if I can.
Good luck & happy listening.

I don't really have any corners to speak of, and since my room is large enough I've been told off-line by a knowledgable person that I don't have typical small-room bass issues, but I do have an 8' free standing wall about 3' behind my head I think I will address.
To this point, thank you all for your assistance. It really helps to hear from folks who've lived through these experiences.