I put mid priced Alpine head unit from Crutchfield in my son's pickup for him. Came with the wiring harness and everything with it. Took about 20 minutes to yank the old one and install the new unit. Like night and day.
AS far as subs not working in cars? I don't know about that as I've sat in several audio dealer showcars and some competition cars and yes, they will play loud enough to blow your eardrums (heck, I can do that with my stock speakers in my stang), but they also sound exquisite at lower volumes and the subs fill in that bottom end just like home systems. Most subs in cars just do that rumble thing and sound like junk because they aren't EQ'd worth a darn. EQ's are indispensable IMO for car audio. One of the best systems I've ever heard was the Clarion rep's car. He had 4 6.5" woofers he was using to augment the bottom end, each with a 100W amp to them. Bass was low, tight, and fast...just like a good live show. I've not heard a home system yet that has come close to touching it. And I have no idea how those little speakers were able to reproduce the low frequencies that they did.
Point being he can do damage to his ears with about any car stereo, doesn't have to have subs. And a good idea above to let him have his $0.02 worth in picking stuff out.