I have upgraded the sound system in my GTi gradually over the last year very successfully and with minimal modification to the car. It sounds fantastic now and I would recommend the following configuration and equipment to anyone looking for a good quality audio system with minimal modification to the looks and functionality to their GTI.

I used the standard head unit (Blaupunkt 2040) with the optional 6 disk Clarion CD changer, which means the existing mulitfunction display and controls operate as normal. The only modification involved cutting the back out of the plastic speaker mountings in the doors to accomodate the larger speaker magnets and cutting out the grid part of the black plastic covers to flush mount the larger tweeters that I used. Other than that everything is standard and all speakers are installed in their standard enclosures behind the vehicle's standard grills, so nothing is visible to prying eyes !

Although the standard radio's output is pretty pathetic and has no RCA's, it can be connected to a preamp via the standard speaker wires and then into a decent amplifier. I used an Audio Control 3.1 preamp which includes an equaliser to shape the sound and a Rockford Fosgate 400a4 50wx4 amplifier. Its important to get a decent line voltage coming out from the preamp into the amplifier so that you get a strong signal. 3-5 volts is recommended and this can be set on the preamp using a voltmeter.

I replaced the existing front speaker splits with the Rockford Fosgate FNQ2614 6.5" component split speakers. These are a truly kick ass set of speakers and I definitely recommend them. They can easily handle anything thown at them and do so with amazing clarity and zero distortion, even at volumes which make your eyeballs rattled in their sockets !!

In the boot I have installed a Rockford Punch HE Series 12" subwoofer in a ported box. This speaker is powered by 2 channels on the amplifier bridged. The rear speakers have been replaced with 4.5" RockFord Fosgate  Power 100 full range speakers with a capacitor installed in line to filter off all low frequencies. Both the front and rear speakers run in parallel off the same 2 channels on the amp. The front speakers are 4 ohm and the rear speakers are 8 ohm. This results in a nice 2/3, 1/3 split in the power distribution between front and rear whilst still remaining above the amplifiers's 2 ohm stability rating. These speakers provide a decent amount of rear end fill, whilst also adding to the general ambience of the the sound in the vehicle.

On the power side of things, the vehicle is still running the OEM battery and alternator. To insure the amplifier always has enough juice, especially under heavy load, I have installed a Lightning Audio Strike capacitor.