I fitted a columbus(rns510) to car. This caused major flaw in sound quality as speakers distorted when volume is at 35%.
So much so I blew a rear speaker and tweeter. I have since upgraded to some ground zero components which fit perfect and sound amazing.
I only did rear speakers as this is where system lacked and distortion was coming from.
The rns 510 has 25rms second stage amp.
I can assume your BASS and TREBLE on the radio where turned up to the max.
I'm yet to see someone blow there factory speakers or amp, unless turning their bass+treble to max then turning the loudness dial up.
that = certain death for Speakers and Radio.
to the original poster. I too am guessing your over powering sound is coming from your sounds settings turned up in the car to compensate for our lack of sound with the older RCD300/500 series radio's.
Hell my factory speaker in my old MK4 and now for a few months in my mk5, happily ran at 150WRMS into the factory speakers front and rear.
Happily shows it's not lack of power problem. More so a speaker settings being adjusted outside of their physical realm of ability.