Hmm... Scary. If the impedance is not it, then that suggests maybe the speakers are out of phase. That can happen if the harness is wired wrong. And we already know from prior experience that Hansshow definitely sent out harnesses that were not wired properly. It seems like a pretty common problem, but I can't tell if everyone had it or not.
Trying to think of other reasons it might happen. One might be that the DSP settings on the F setup are wrong. Or that getting them tweaked to match the audio they want makes some speakers excessively loud. For example, the chime frequencies are boosted way up in order to make the music sound good.
Oh wait- you have
@todd2fst4u amp setup, right? AFAIK Todd doesn't do the doubling up of speakers in parallel. That's the point of using the 4 channel Alpine amp, to get discrete channels for each of the new speakers and not break the impedance. He uses the TeslaOffer or Hansshow harnesses, but cuts them up to make his own harness.