In that case; the speaker outs on the head unit are line outs via a pre amp.

Crutchfield offers Line Output Converters (LOC's.)

I don't understand them very well.So I just stole this from google ai:

A line output converter (LOC) is a device that converts a speaker-level audio signal to a preamp-level signal. This allows you to connect an amplifier to a factory stereo or radio. LOCs are also known as high-to-low converters, speaker input adapters, or line level converters.

So it seems like it's unnecessary in this case.

Maybe. Seems to me that using a LOC for just the sub would introduce latency into a mixed system, a horrible situation. But my (further) thoughts are useless because I don't really know what I'm talking about.

OP needs to figure out how to discern who actually know their 5#!+ from the 95% who think they do, or know perfectly well that they're clueless but like to bs. (Looking in the self-examination mirror.)

SNAFU

What I know is that the method in the post I linked to works.

I don’t doubt it.

I'm not sure if you guys will get notified but, I got them installed! I was way overthinking everything and ended up just following the sticky post here, everything works perfectly and I couldn't be happier with everything, thank you guys for your advice and input! I'll try to make a post of the install once i fully have my hatch put back together lol, the subfloor pieces are still out lmao

Thank you for your follow up, confirming your issue is resolved!!

Be sure to take pics before you put it all together! The wiring in particular.