Ok, I visited Best Buy. The electronics folks were obviously inexperienced with audio. They had no opinion on Head Units or amps, other than price and specs. No help on subs, as all they had were two kickers, and it was actually the same model, just one in a stock enclosure and one in a different enclosure. They had a JBL sub, but it was not hooked up to listen to.
They had the following brands to listen to for speakers: Kenwood, Kicker, JBL, Alpine, and something like "Grand Tour". Of all the speakers they had, I preferred the Alpine S-S65, and by a wide margin. Weirdly enough, I liked it better than the S-S65C. I could see putting SPE-6000s in the back, but they're only $10 cheaper than the S-S65s, so why not just use two sets of S-S65s.
I've become very confused about replacing the dashboard speakers, if I need to, etc. The Best Buy staff had no knowledge or advice about this.
So I dont know much more than before the visit than what Best Buy charges, except I liked the Alpine speakers better than the other models.
I guess that's a start at least.