I have the Bose system in my 06 coupe and im tapping into the speakers before the amp juts like this DIY says:
https://g35driver.com/forums/audio-video-electronics/101293-diy-add-sub-your-bose-equipped-g35-coupe.html

the problem i have is that the sub is barely vibrating, i dont think the sub is getting a proper signal.

Ive heard mixed stories on whether to use a Line Driver or a hi/low converter or a LOC???

what do i need betweeen the speakers going into the Bose amp and my aftermarket Kenwood KAC-8103D amp?

 

See your other post.