Oh no, not big dollar, for a 4 channel to run your components a nice used amp will more than suffice. Hell you could almost replicate my system (minus some of my wonky experimental stuff like the flat speakers) for under $500 total easily! My main drivers (Vifa PL) are worth $25-$30 each, my tweeters (Vifa Logic) came in under $30 each and are extremely impressive even comapred to some $200 tweeters. An HU with time correction will slot in around $250-$300 and the 4 channel amplifier (if you even decide need it, most aftermarket HUs will make a huge improvement over stock on thier own) and then all you have left to consider is a sub and amp later on.
Just start simple. Get these Kappas in and running and see how they work. Figure out what you want to do from there. In my experience the best route to go was
- New head unit, go mid range. Most mid range HUs have all the features of the higher up models minus some fancy screens or extra features that may or may not be useful. Time correction, built in EQs and a good crossover are important. I always plug Alpine HUs because I'm used to them, but try them out for yourself and decide from there. Look at about $300 for a good unit with useful features.
- New speakers. Components are a must (you already have them). They cost a bit more than coaxial speakers but the tuning and placement options are worth every penny. It also gives you the option to amplify the tweeters and mids seperately. The first thing I do it switch my HU to 3-way mode which means no rear speakers. That's because I hate the people using my back seats (which is why I put them back there in the first place) and also because rear speakers ruin a good stereo soundstage by drawing everything rearward. By switching to 3-way mode the head unit will adapt itself to better run your front stage. If your rear passengers want music tell them to walk, rotten ingrates.
-Subwoofer/Amplifier. I am not a fan of 5-channel amplifiers. I always dedicate an am to running a sub on it's own. They usually take a much bigger beating than the amp running your speakers so if it dies, you can still have music while you are finding a new sub amp. This is where things will finally start getting more expensive, you need to run the wires and all that fun stuff. There are two ways to do it. Wiring kit worth $20 from Best Buy, or waste $300 to make everything look fancy. They both work the same, one just looks like it works better.
- New custom front stage. Pick parts from the entire world of audio to build your own component set, I went with a 3-way front stage (tweeters, mids, midbass) and went over response graphs, ratings and all that fun stuff to pick parts I think would work well together. I also like wierd and different things so I went with parts that I've never seen used in a car before. By picking parts that work well together, you can get a huge improvement over a boxed set of components, and it doesn't have to be expensive either, you just have to understand what you're looking for from each speaker.
- Surround sound. I never saw the point of this in a car, but if you have a screen for movies, or just really want SS then yeah, you need to buy new parts for each corner as well as the center channels. I'll stick to stereo.
-Media Controller/Car PC - At this point you have probably gone through a few different setups, and want absolute control of the whole thing. This is when you pick up a media controller to fine tune every single piece of the system, or build a car PC that does the same thing through software. When you get here, you'll probably not be reading my posts anymore because you will be too busy reading posts by some actual audio gurus
