I decided to upgrade the old Pioneer custom fit components in the front doors of my A4. I bought some Rainbow SLX-230 deluxe 13cm units with silk dome tweeters. Well 4 hours later and I have one side completed. It was a real bitch of a job as the new woofers are designed to be front loaded and I had to heavily customise the MDF adapters that I made to get them to fit properly. Also had to slice a few mm's off the inside of the door to stop the panel fouling on the speaker chassis. Well a roll of Dynamat and a few hot melt glue sticks later and.... TBH now I can fade left to right and do a direct comparison there is very little improvement at high volume. The Rainbow components still sound a little harsh when driven hard (via an Alpine 4ch amp, HU & CD changer), and the benefit, if any, seems to be pyschological (they're better speakers so they must sound better). I wouldn't do this upgrade again, and just proves what I already thought that there is a limit to the quality you can get out of a front door speaker, and that limit has nothing to do with the speaker itself but the acoustical limitations of a hardboard door card loosely screwed to a metal tin can. No amount of Dynamat or money spent on the speakers can change those limitations. I'm sure there are some audiophiles who will poo-poo the above and come up with any number of theories as to why the upgrade is worthwhile but I can only report the facts and literally can't face doing the other side for such a minimal improvement.