On 2007/2009 GM, Which Module Is Responsible for Translating SWC?

Steering wheel control buttons - how do they work? Any GM Engineers lurking?

Figured I'd post for the experts. I'm very curious what is the deal on the following.

On many 2007+ GMs you can retrofit an updated heated steering wheel.

I've got everything working, new clock spring and all, but the stereo buttons are my last problem. They changed the SWC controls between 07 and 08, and the new ones work, but they all have the wrong function. Ex, vol down changes the source. vol up activates onstar.

I've done a ton of research on this without clear answers.

I flashed the BMC with a 2008 flash, didn't change how the buttons work.

I flashed the IPC with a 2008 flash, didn't change how the buttons work.

I flashed the Radio and AMP with a 2008 flash, didn't change how the buttons work.

Here is what I know: it's a single wire for all the controls. When you press the buttons it varies resistance on that wire and that's how it knows what to do. I just can't figure out what friggin module does the translation, or if I have any hope of fixing the assignment of the buttons through flashing or modifying anything?

Am I wrong to think this is a flashable thing that can be programmed with a Tech2 or SPS or is this really some additional part, or a different part that is needed. The part numbers of the BMC and IPCs *did* change between 2007 and 2008. Thus far I've tried a 2008 BMC, didn't fix the issue, I have not tried a 2008 IPC.

Any thoughts?

OEM or aftermarket radio?

https://www.bbbind.com/tsb-wiring-diagrams-database/

2007 Malibu:

https://www.bbbind.com/tsb-wiring-diagrams-database-results/?type=WD&years=2007&make=46&makeDesc=Chevrolet&model=423&modelDesc=Malibu&docid=7522877

2009 Malibu:

https://www.bbbind.com/tsb-wiring-diagrams-database-results/?type=WD&years=2009&make=46&makeDesc=Chevrolet&model=423&modelDesc=Malibu&docid=7844466

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My ex once told me I have a perfect face for radio.