Need advice on my sound system, Speakers, amps, subs Options

[shid]

Hey guys, I'm looking to upgrade my sound system and have been running through a couple of things.

My main goal is to have a system I can hear on the freeway, going 90, with the top down without distortion. I don't need to win decibal drag contests.

I mostly listen to rock, techno and rave- with a few rap and R&B songs stuck in to make myself look like an idiot.

So, I was thinking to just amp the subs, and not amp the speakers? (I have a stock amp in there, but I don't know what kind of power that puts out).

My current headunit is an Alpine9803 with 50Wx4 and 2 preouts. I don't plan on changing it with my new speaker setup.

As for my new speaker setup, I was thinking that for the front components:

Polk Audio db6750 or
Alpine Type S SPS171A

For the back:

Polk db675 or
Infinity Kappa 652.5i

I'm learning towards the db6750 for the components, and the Infinity's for the rear.

Now, for the subs, these are going to go in the trunk (unless someone has a better place to put them besides the front doors). And I need to hear these with the top down- BUT, I also need my trunk space- so nothing too huge (or heavy, preferably).

What can you guys recommend for an amp? I'm not looking at anything too expensive, but I don't want it to crap out on me.

Amps?:

Sony XM-D500X ooorrrr.. I have no idea, I have no idea what I really need

Subs:

The space issue is making me consider tubes a lot more than sub boxes. I just don't think I have the room for a sub box- no way. I was also thinking 8 inch or 10 inch- I don't listen to rap a lot so there's no need for a 12- and the 10 or 8s provide better sound for rock and techno anyway right?

Maybe 2 Bazooka RS104DV (10 inch 250w per coil)

Whats the benefit of more power to a sub? louder? What would 2 subs get me vs one?

Please help

Oh yeah, and any ideas where to put the amp?

--Sean