Speakers/Head Unit AFTERMARKET

I'm wondering what kind of aftermarket stereo equipment we all have in our svxes.

I'm looking to upgrade my speakers and head unit, but dont have much knowledge on the specifics. My SVX has the door speakers and dash tweeters. I was unsure of if the tweeters should remain connected after a speaker upgrade?? Or perhaps it is possible to buy tweeter upgrades as well (not that I would or would want to after a speaker upgrade, since the new speakers should be more than sufficient).

Are there certain headunit brands out there that don't fit in the SVX or that don't install properly?

What about speakers? Anyone install any decent sounding speakers from BestBuy/Circuit city or have problems installing certain speakers??

I figure I'll ask other SVXers about all this since the 'techs' at those stores most likely know jack and sh*t (and jack left town) about what works for the car and what doesnt.

Those stores are less expensive and more customer friendly (in my experiences, others probably disagree) than your privately run auto sound store, so BB/CC is where I'll be obtaining and having my stereo upgrade installed.