"So darn bright :( something wrong here...."I’d have to agree that it sounds like something is wrong here.
"... if this was their sound no one would like them and so many people do!"
This is probably a long shot, but it seems worth asking: Have you been running the Sumiko subs with the Magico speakers? If so, and if you are connecting the subs at speaker level, have you been connecting the black wire of the Speakon cable to the white signal ground terminal on the rear of the amp, which is where it should be connected?
If instead you have been connecting it to a negative output terminal of the balanced Pass amp, which is a mistake that seems to often be made when connecting powered subs to the outputs of balanced amps, I’m envisioning that in combination with the low impedance of the S5 (as opposed to the impedance of your previous speakers) an ultra-sonic oscillation could conceivably result, that would manifest as brightness/harshness. And that kind of effect might account for the sensitivity to the amp’s power cord that you mentioned.
Just a thought. Regards,
-- Al