Nakamichi has never made a real good auto product. And Eclipse is so, so. I would give Infinity reference series, or some Polks a looking into. They're a bit more, but my Infinities were great. They're very efficient, so running them with the factory power is not a problem. When looking at speakers the higher the db sensitivity the more efficient the speaker. One's with low #'s will probably require extra power. Most of the component systems will require an amp to get the full potential out of them without distortion at high volume, whereas
most standard 6x8's will not. Just be careful of companies that give some great specs...i.e. 3,000max watts, 12 way tweeters. If it's sounds great, they're probably lying. Spend a couple more bucks and get something nicer. They'll sound much better, and will last longer. Most speakers will sound good in the store because they're mounted in nice wood enclosures, not door panels