Don't move your speaker after you place the treatments at the reflection points unless you also move your listening position to get back to that same reflection point. So get the speakers placed first where you want them, IMO and IME. (BTW, I would move the speakers farther away from the side walls. Have you tried placing them 1/3 third of the way into the room and then move them out until the soundstage looses focus?) The absorption panels will help with the slap echo, but I have found that the best treatment spot for this effect in my own room is in the corners and all wall/ceiling boundaries.
Everything I have researched says it is near impossible to have too much bass trapping in a room, as long as the treatments are also designed not to absorb higher frequencies. I believe this means that to get to an over-damped sound you would have to start killing the frequencies about 1 or 2kHz, so research the treatments you are going to use. It is usually easy to prevent this from happening.
Also, check out the acoustics forums on AA and AudioCircles. Free advice from the Pros there!
Everything I have researched says it is near impossible to have too much bass trapping in a room, as long as the treatments are also designed not to absorb higher frequencies. I believe this means that to get to an over-damped sound you would have to start killing the frequencies about 1 or 2kHz, so research the treatments you are going to use. It is usually easy to prevent this from happening.
Also, check out the acoustics forums on AA and AudioCircles. Free advice from the Pros there!