Freaky speaker experience:

Had the same experience with a pair of Avalons back in the 90s..never knew why

Any chance you had one set of drivers hooked up out of phase?

I'll second Rleff. Sounds like one of the woofers was out of phase. If everything appears connected right I might go so far as using an ohmeter and checking the cables.

If she's game, perhaps your wife could change from single to bi-wire a few times without letting you see. She should also not change them at all, just pretend to, a few times. Then do the same for her.

I'm open to there being a real difference with bi-wiring (that couldn't be achieved with a single run of the equivalent gauge of a single wire), but I've never heard a convincing explanation for why there might be a difference. The explanations always sound very hand-wavy to me. I'd like to seem some actual math.

Even so, I made some "true bi-wire" cables for when my new Vandersteens come. Cost for materials was under $40. By "true" bi-wiring, Vandersteen means keeping the two runs separate by at least an inch instead of having them in the same jacket. But I did this more because I could than because I expect to hear a difference.

I'll third Rleff.

Regards,
-- Al