Is Bass Non-Directional In A Two-Channel Rig?

I'd be interested to know if your test people that evaluated the soundstage difference would have different results using a single subwoofer. I suspect your ability to pinpoint the subwoofer is much better than even the above average Joe.

I have had a number of people be part of this demonstration some listeners with a great deal of experience others who think an I-Pod is highest of fidelity. None however with just a single sub. Tom

How can you be sure that the difference in soundstage results from having two stereo subs located as you have them and not just a result of any sub placed anywhere?

I have modded pairs of subs before...one at a time. I always had one to listen to and ran it in mono. I left the sub that played in the the same position as when it was part of the stereo pair. I also have a Velodyne smps digital eq which is mono only and eq'd and ran my current stereo pair of subs from this digital box. I had more bass but a worse sound stage and bass tone that was to me less life like and enjoyable. I removed this box from the system. Tom

Yes, assuming that levels are matched, you have a 4th order electrical low-pass filter, and your sub-woofer is free of distortion, port noise, and rattles

One caveat is that stereo bass with phase differences between the two ears can create a sense of envelopment although you can't localize it.

The counter argument to that is that random, asymmetric placement of multiple sub-woofers produces more uniform frequency response above the room's fundamental resonance and avoids one-note bass problems.