Acoustic foam/room treatments - help/opinions sought (N. Abstentia?)

[dmb_fan]

I figure behind the 1st reflection points for all speakers are most important. Then probably some treatment behind them? And the ceiling?

You're exactly right. In order of importance: 1) first reflection points 2) the wall behind the speakers 3) large reflective bare walls (and your ceiling is the largest of these).

Definitely take advantage of Auralex's expertise by surfing their website for placement recommendations. Note, however, that most of these recommendations are based on setting up a recording studio or a mastering table, so you'll have to use common sense to adjust for hi-fi.

Generally speaking, flat foam will do best scattered randomly with a concentration toward the middle of the walls, near ear level, and away from corners. It's really only style that requires a pattern. For use in a hi-fi listening room, you'll want to pay special attention to initial reflection points to stop them from detracting from imaging and special attention to other bare spots at the tweeter/ear level for the same reason.

I was thinking of cardboard, but it might be too thick? Or bristol board or something? Any other good ways to tack this stuff to walls?.

You might try these: http://truesoundcontrol.com/products/TEMPTAB.html

I'm jealous! The stereo room is also the living room at my place, so the wife isn't about to let me turn it into a padded cell (even if she thinks I belong in one). You should notice a significant improvement.

Don't forget to report the results. With photos!

Have fun,
Adam