my recommendation would be to first consider how much effort you want to put into the speaker mounts if you are going to use an amp.
I've stuck with head unit + speakers only because if you up the power to the next level you are asking an awful lot of the OEM mounting points to give you good sound.
e.g. mounting the front drivers onto the door cards has its limits, it really needs proper mdf door pods, which means cutting the door skin (something I wasn't prepared to do).
If you're not to bothered about all this then I would say the Rainbow kit (as per my install) will be fine (don't set the amplifier gains at their highest though) or if you want even better sound then go for the JL Audio XR 650 drivers.
