Car hi-fi installer in South Wales

Basically I'm looking for somewhere in south wales that can be trusted to upgrade the sound in my E46 BMW. For anyone who has one they will know how rubbish the factory sound system is. Cardiff would be preferable but I don't mind travelling. Recommendations from first hand experience would be appreciated. Sensible prices and labour charges but most importantly someone who will look after the car and treat it like its their own.

Thanks

All of the speakers will need upgrading, I'm after good quality sound that can be played relatively loud (but not excessively) without distortion and without being harsh on my ears. Full range of sound is important so I'll probably need at least a 10inch sub. Again, quality of bass is important as opposed to something that is going to shake the car to pieces. I also want to keep everything looking stock (apart from the sub in the boot obviously) which does complicate matters a little.

I don't really want to spend more than a £1000 not sure if I'm asking too much from my budget.