Answers for the above 3:

I have double checked the wiring (when in bridged, the single speakers connect to the 2 outer terminals of each zone)

I lost my impedance meter so I tested with ohm meter ~ around 8ohms

During the testing, I moved the amp to the speakers and connected directly with 5ft 14awg wire, to remove IW from the picture.

Turning the output gain of the source down? - Tested with high end Denon CD/Media player, 2volts output, which standard. I have read the document for the gain dial but in my case - the document is worthless as the amp "self protect" against such issue. Again, input gain on the amp was at 50% max (it starts going into protect pass that).

My guess: Document is old, they have updated the amp and it now has more aggressive protection.