I just got a 2001 Audi S4 with stock Bose stereo that *****. I think I'll need an adapter kit to go single or double din. It has 4" front door mids with a tweeter by the handle, but can take 5 1/4" with an Ebay adapter. Rears are either 3 1/2 or 6 1/2", though I plan to just leave them stock and run them off the head unit. There are also 6 1/2" "subs" in the rear deck that I'll take out (not sure if I'd need to block out the holes or I should just leave them unplugged).

I am looking for everything. I think double dins look nice, but I would never watch a movie on it and the premium for navigation isn't worth it over just using my phone, so I'll probably just go single din and a storage pouch. I'd like USB to use a thumbdrive with as that's what I've been doing for ~7 years. Some kind of auto calibration would be nice (I would think at least) if I go all out.

For speakers, I'm not sure. I'm torn between just replacing the speakers with 2-ohm Infinities or using and amping whatever I want. I haven't heard or been looking at much yet, but I've listened to Focal K2 Power components in a showroom recently and liked them. I'm open to suggestions, something that's not too harsh. Not sure on available mounting depth.

Amps, I'm not sure at all. I'm guessing I would just do a stereo amp for the fronts and a mono for the sub. I have a Kicker ZX750.1 if I can use that for my new sub.

Sub, no idea. I want it to fit in an enclosure that would fit in my tool/cd changer area in the side of my trunk to retain trunk space. I have a pair of 12" Kicker CVRs in a Kicker box now and and starting to get tired of that. I'd like to go more sound quality now, though still decent output.

I listen to rock and rap mostly. Budget is flexible, I'm not sure what I'd like to do yet. Different price choices would be helpful. Maybe a couple hundred for a head unit, couple hundred for speakers, couple hundred for sub, not sure about amps.

I'm kind big into home audio, so I figured my car should sound decent at least. Before I was big into home audio, I had some amped pioneer coaxials in an explorer that I thought they sounded pretty good. I ran wire straight from the amp and installed myself. Then I had someone bypass the VW amp and install the same speakers in my Passat and they sounded pretty bad. I think the speakers in the S4 attach to the door panel only and not the door frame. If it's going to take a lot of modification for the new speakers to not just shake or rattle the door panels and sound like crap, that would be a big factor too. I will be doing the install.

I am fine going with used if it's safe to do and people don't often try to sell broken/abused stuff.

Thanks for any help

edit:apparently you can't say su.cks, haha