First decide what you want. Sound quality or loud sound?(that will still sound crystal clear, just not as REFINED. Think club.)
I suggest you do it yourself if you want to stay within the $500 budget and have a half decent system. Look into some pro loudspeakers. Either 6 or 8 inch. 1 of those will be as loud as 5 car speakers //content.invisioncic.com/y282845/emoticons/nerd.gif.c6fa51ddf7ff75f1c0371fbc648f70ae.gif They can be had as low as $30-$50 a piece. Door treatment is a must. I suggest 4mm vibration dampening mat on outer part of the door and inner part.
They are not as loud as 5 speakers. And the $50 are horrible with nasty cone break up and next to no bandwidth
You have a very nice HU, Just switch to network. It's not all that complicated. You can always ask if you're not sure about something. You can learn the basics of car audio in 1-2months AS you go.
What's so hard about adjusting crossovers? Mid filter on that HU should have a bandpass mode, you won't even need the amp crossover, it will be used as backup. Mids can play from around 80hz. If you wanna blast it you set HPF on the HU to 200hz. As for tweeters they play from 5-6khz. You use amp filters as backups for your HU filters. Say HPF on the headunit is set to 150hz for mids, you can set it at 150hz or a little lower at the amp as well as a backup filter.
I guess these settings are so high because your speakers can't play midbass. Tweeters that high will make mids sound horrible[/i]
you will need separate amps for mids and highs. 2 2channel amps is all you would need for 2 mids and 2 highs. hell, you could go with a monoblock, just won't have stereo. having 2 separate amps for mids and highs is crucial cuz your HU will send out different signals to each amp. once you get it installed tune the amp sensitivity/gain/level. Every headunit has a volume where it begins to distort. Your job would be to find that volume with the gain turned all the way down and then play a 1000hz sine wave while turning up the gain. Once you hear the sine wave distort, turn it back a little. A 4 channel. There are very few full range mono amps on the market and they all have big roll off up top, you just told him to only play 20-300 or so Hertz
If you wanna go this route I'll be glad to help where I can.