Originally Posted by RichieST

Ditch the power cap. They do nothing apart from add a bit of bling and cause potential problems. Don't use 6x9s either, any speakers on the parcel shelf will distort from the bass in the boot. Keep standard speakers in the back just for a bit of rear end fill and spend your money on good quality front door speakers and amplify them properly too. Don't forget sound proofing and use quality cabling, this will make the best of your equipment. A £50 pair of speakers that are amplified, wired and fitted properly into a sound proofed enclosure will always sound far better than a £200 pair of speakers that you've just chucked in.