Speaker Placement

So by 160-170 degrees relative to the listening position you mean firing almost directly away from the listener? There are some speakers with ambiance drivers that are aimed backwards and Bose speakers certainly adhere to that philosophy but it would not be good for sound stage reproduction. I admit that I haven't tried it and it would certainly be affected by your room (reflections) but I can't believe that it would be good for more than background music.

I'm sorry if I misunderstood you Roscoe50 but when your reference is 60 degrees off-axis (i.e, an equilateral triangle), 160-170 degrees IS sitting almost directly behind the speakers.

In regards your response to what Manitunc is saying, the nature of stereo may be two point sources, but the nature of hearing is not. What we all (supposedly) are trying to achieve is a reasonable facsimile of the original performance using those two point sources. In my experience headphones do not do that. Although I do occasionally listen to headphones, there is no way I'm giving up my speakers (arranged in a slightly isosceles triangle) for them.