Damn i wish i knew about this place before i had to have my entire engine replaced. I paid around 2grand though and thats with labor. So i guess i did good.
So i contacted Subaru of America asking about the VDC/ABS and they said this
"The HK audio system in a 2009 Legacy Sedan does not have VDC/ABS sensors."
Idk where you got those wiring schematics from, but I cant seem to find any info stating VDC/ABS is tied into any factory amp.
In fact ive found more threads with people trying to disable VDC/ABS and none of it has to do with the audio system.