I have a 2017 Jetta GLI and I want to add a 4 channel amp to bypass the fender amplifier. I want to retain the MIB2 headunit.

My goal is to get high or low level speaker outputs directly from the radio (MIB II) at the brown plug. My current problem is that the radio does not change the gain / volume on the output and only mutes with the volume all the way down. It does this since the speaker volume is currently adjusted by the factory amp. I have read that it is possible to do some coding to change the type of speaker output coming from the radio.

I want to buy a VCDS tool, but want to confirm that I will be able to do what is necessary before I spend the money since I could buy an aftermarket headunit for the price of the tool.

Here is a video of my current issue. I have the subwoofer hooked up to the outputs coming off the brown plug to demonstrate the lack of volume adjustment. In the future, the 4 channel amplifier will be connected there.
https://streamable.com/e9ifr