Try the CARA software to guide speaker placement. It has a steep initial learning curve and requires hours of "work" at your pc but, if you consider how many hours you'll devote to listening in the future, the investment in time is well spent. My best CARA tips: 1.) make the effort the accurately "build" your particular loudspeaker, if not in the (very sparse) existing list; 2.)weight
"frequency response" a 10 and the two other variables 1 or 0 when running the positional optimization part of the program; 3.) also, when running positional optimization, run SEPARATE trials for bass, mid and treble frequencies, with the goal of getting a position where the "quality" percentages agree most closely. To accept an "optimized" position derived from the full frequency spectrum of your speakers (I found) can hide potentially terrible acoustical performance in one or more smaller frequency bands.
Again, just my 2 cents.
John

