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

No I have never tried that. It would be mixed mono and not stereo and there would't be the close chance of aligning the voice coil of the mains and the subs. I have used a single sub of the same pair while I was doing a mod on its mate. The single playing sub was not moved and I could hear where it was placed even in mixed mono. I think at that time it was the Paradigm Servo 15 pair. They always have flanked the mains. Tom

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