Unusual Mazda6 issue - dealer not able to solve starting issue after audio install

First post on here after a lot of research without success.

Looking to see if anyone else has encountered this before....

Car: 2014 Mazda 6 GT

Recently did a basic installation of a subwoofer and mono amp - all electronics work after install but the car won't start.

Initially the car error was key not found, as well as check system messages for every system on the car.

Reprogramed the keys and car still wont start.

The battery was fully disconnected during the installation- we have checked voltage and even tried jumping without success.

Installation was line out converter tapped into the bose harness for FL / FR door subwoofer and the 12v remote line going into the bose harness. I have even tried taking everything off and it still wont start.

After hours of research and labor we decided to send the car to a Mazda dealer who can't fix the problem and stated they have to call mazda for support.

Is there any system errors that would not allow the car to start because of the bose harness?
2017 Mazda CX-5 GT, 2016 Mazda6 iGT, 2014 Mazda3 sGT hatchback
Does 2014 GT has the i-Eloop? If yes, after batter reconnecting, you might need to reprogram it. Dealer should know that. I am puzzled by that.