I won't be the "looser". 25+ years of acoustics with personal contacts with many of the leading people in the field, a bunch of peer reviewed papers, a deep understanding of the science of sound, psychoacoustics, and enough interaction with the research community, often helping to design experiments, and well beyond the need to prove anything to anyone in my community.
Unfortunately, or fortunately, I care enough about audio that it gets my back up with people who think they know what they are talking about, but have no clue how to even design an experiment, let alone the underlying principles of what they are trying to test, speak with complete conviction and lead other people astray, causing them to waste precious time and hard earned money to achieve inferior results.
While your main seem to be of good quality, the subs are not very good quality. They were inexpensive new, and used are quite low cost. When they say "servo" they don't mean a servo in that their is position feedback on the amplifier, it is just a marketing term essentially for what appears to perhaps be a current feedback output design as opposed to voltage feedback. Odds are the distortion is not insignificant given the cost constraints.
So the left plays for 5 seconds and the right for 5. You still said it took 10 seconds, i.e. one complete cycle. Normally you can tell source location near instantly. You wouldn't have to wait till the switch back to be sure. This is a "really" moment, because it goes back to the difference between actually localizing bass frequencies, and detecting a differential room signature (potentially exacerbated by distortion).
Are you subs placed in close proximity to your mains?