Got a few questions?
 

Alright so I am in the process of deciding on what type of new components I should get for my car which is a 1999 A4 (which already has the Bose components but I need more clear sound so I can hear over the sub)

Here are the options I am considering right now:

Infinity Kappa50.7cs Car Component System (5.25")

Eclipse Components (5.25")

Alpine Type R (5.25")

also if I just get a pair for up front then say later on down the road get some coax Alpine S type for the rear would they all work together if I get a decent amp?

well you have one advantage with the Infinity components, they are a 2 ohm system, which means that all else being equal they will get double the power from the same amp(assuming that it's 2 ohm stable). Theoretically, you should be able to play them louder and cleaner with more power, but I'm sure others will debate it seeing as it's at 2 ohms. I like Infinity speakers, they tend to play the music I listen to very well. That being said, I loved my first set of Alpine type s co-ax's, I think they are great for the price. I personally would stay with the same brand for mid/high speakers for the front and rear. I think they retain a similar sound which seems to blend better than using multiple brands. As far as Eclipse, I've never used them, but I've heard great things about them, and that 3 way system with the 2 inch midrange looks really good for a door/sail panel set up and a 4 way active x-over system. I say go take a listen to all of them and then decide.

Back up the bus a stop there dude. A closer look at the post shows that he has a Bose system, quite possibly and more than likely a hidden factory amplified system. This means that you can't just arbitrarily add speakers to it. Most Bose systems use impedence matched drivers to the factory amp. Some of them also use indipendent channels of amplification for the stock woofers and tweeters. I would find out first exactly what the stock system is comprised of. Then I would make a plan of attack on how to add to it. Chances are that you will need to ignore the factory amp altogether, adding a interface adaptor, new amp and new front speakers to make this work. Then you would need to do the same for replacing the rear speakers and finally a sub if you see fit.

Now, this of course is provided that it is a amplified system which it probably is. I would look to a interface adaptor like the Audio Control LC6 or 6XS so that a proper interface is used and this will allow you to expand with ease at a later date all the while keeping the stock head unit and balance of the system in use.

You can't miss on many of the good speakers these days. The Eclipse component have been amazing speakers for years now. Good tonal response is not just about the speaker, it is also about how it is mounted, how they are interfaced to the stock system, the choice of cd's and of course, how you hear.