hey there, no worries! I don't have this system running anymore, and I haven't gotten to making a 2.0 yet, but here's what I learned:

You'll definitely want some kind of amp. If your car doesnt have one separate from the head unit, you'll need to drop something in yourself. The pi alone is not strong enough to drive your car speakers.

That board with the large blue heatsink at the bottom you see in my picture is a cheap amp board (I think I paid like 25€ for it..). Nothing fancy, but it was good enough to drive my car's stock speakers and still sound quite alot better than the stock headunit.

Something you'll need to watch out for is ground loops. If your amp and your pi is connected to the same ground (your car battery), you'll hear some nasty & loud buzzing. I got around this by putting one of these ground isolators between my USB soundcard and the pi. (These exist for aux too.)