What have you got now? You won't need an amp unless you install some sound insulation in the doors. Just get the spacers, iso adapters $150-$250 speakers and a source unit that has integrated Bluetooth.
I've got Pioneer TS-C components up front an cheaper TS-D co-axials in the rear. I cut up the foam in the front doors and wedged the crossovers there. My source unit is the ICS-X7 by Alpine. I find that a lot of the bass is drowned out by road noise so I recommend insulating the doors to get the most out of your speakers and for a quieter ride. FYI, the X7 is a bit laggy but it's much simpler and less gimmicky in comparison to a Pioneer source unit. If you want speakers better than Pioneer but don't want to pay more, get Focal speakers.[/quote]
Or, instead of focals and want something with some midbass and not just piercing highs, go with morel or crescendo.
Regardless of whether you run the drivers off an amp, you will want to invest in some sound deadener. Not sure who's telling you that you can't run an amp off the factory head unit. They clearly have no idea. All you need is an amp with high level inputs, most if not all do nowadays. Or you can use a line out converter but they induce a shit load of noise. Not sure if that has been covered before but there so many threads in the audio section that cover all this before so haven't really read all the responses.[/quote]
+1 ...but I'd only keep the original source unit if you're happy with CDs and don't want to fork out another $350 for the fascia kit like I did. My install without an amp and sound deadening was about $1500 all up. Most would think I'm stupid for spending 2/3 of it on the source unit but I love the touchscreen and Bluetooth capability.[/quote]
Nope... Never thought it was stupid to spend 2/3 of 1.5k on source

Its only now stupid if u dont go ALL THE WAY n upgrade the rest hehehhehep