Best speakers for 98 ss?
That's my .02
An amped system is really the best way...
That's my .02 
I tried to do the same thing as you, I didn't want a sub, just decent bass from my speakers. Boston acoustics run a couple of hundred per set and you get decent bass from that. You'll never get decent bass from normal speakers unless they are super high quality (and super expensive) and typically components. It's pretty much impossible to get any kind of bass from coaxials.
I bought a 12" alpine sub powered by an alpine amp, both modest not the crazy stuff, and i get decent bass. Only reason I went with a 12 was because I already had a custom fiberglassed enclosure for a diamond audio 12" sub which he put a drill through while drilling it in (by the way, use a screwdrivers when you install it)
Keep in mind that bass is largely a matter of surface area, hence why tweeters are so small. If you really want bass, buy a decent 10" sub and if you want you can email me and i'll tell you how to custom fiberglass it into your trunk to make it look flush. Here's how mine came out on my honda:

or you can buy a speaker box. They say 10"s are for bass inside the car, 12"s are for outside the car. i only have one (and only need one)
The amp rack holds the two amps as seen in that picture. Total cost of custom project? $100 maybe.


