Alpine KTP-445U and OEM stereo

I recently had my speakers in the CX-5 GX with convenience package replaced with 6 speaker setup and now i want to install a alpine universal power amp for the head unit. I don't want to cut the factory stereo harness in order to cut in the amp so i was wondering if anyone else has done this sort of similar install using a male end wiring harness adapter and female wiring harness adapter (though the only ones i could find on Metra did not include all pinouts because most wiring adapters are just for speakers and power) and then splicing in between those adapters the amp to make the install plug & play.

Does the stereo factory wiring harness have the steering wheel controls and power on amp pins?

For the effort required to fit that low spec amp - you should fit something decent and just cut into the speaker wires. It will be easier, quicker and sound louder and better.
You can get some really powerfull class -D amps now smaller than that Alpine brick. Don't get me wrong - I like alpine stuff - but that amp will not do the job in this big car.

The factory harness does have the steering wheel wire, but I understand that the power-on may be part of the CAN bus protocol. Which wires does the Metra connector set not have? Some wires are not populated, so it may be that those are the ones missing from Metra's.

This is only part of the radio schematic, but you can see the main speaker wiring connector, 920-401A (pins 1x). Any pin shown with an asterisk, means it's not populated: