sorry in advance for the lecture,...nobody has picked up the torch yet, and...and sorry for telling you stuff you may already know.
Which ever way you finally choose, It won't matter one bit how good the equipment is if the source (in this case the ipod) is bad. You have several compression rates to choose from when you buy or download music from itunes, or transfer CD music that was ripped into your computer.
"CD quality" compression is 320kbps. From there the bitrates drop to 192, then to 128. Anything less that that is AM radio quality, (some internet radio stations are streaming at rates less than 128kbps, and they sound awful)
The reason there is different compression rates is: The lower the compression rate, the more space there will be on the hard drive for music. Obviously there are a bunch of People willing to sacrifice sound quality for that extra space.
AND most people are oblivious to the degradation, because they are referencing that sound quality through a tiny pair of ear buds that don't have a prayer of truly replicating the sound quality anyway.
All this goes to say,.... you know how your music was transferred to your player. If it is all high quality transfers, then your good to go.
The best sounding systems I have heard personally all have separates for the drivers (that is a woofer and tweeter separated w/an external crossover. packaged as one speaker....like a 6" woofer/1" tweeter) I had two pairs of MB Quart speakers like this w/ slightly different sized woofers( 5.5"/6.5") to help cover the BASS transition so the subwoofers weren't so boomy
Of course, The head unit, a 4 channel amp to drive the speakers, two (or more) tens/twelves with a dedicated amp. ancillary batteries/capacitors depending on your need for current, all go with the speakers.
Car audio is all about preference. for that matter, all audio is a matter of preference.What sounds great to me, might sound like crap to you.I hate sloppy, boomy, rattle you guts out bass, Instead I want it tight. I want it to hit me so hard my nose will bleed. Different cars will sound different w/ the same equipment because of the variances in their shapes/sizes. The same car will sound different if it wasn't prepped exactly the same (use of sound deadener, wire size, charging system)
Listen to a few, get a budget, find a good shop to install if you can't and jump off in it.