I thought the stock speakers were made by JBL. But maybe the Euro model has different speakers than the US model. I really can't believe that my rear speakers are 12W (according to pic above). My speakers are driven by 150Wmax amps (per channel) and it sounds really great.
Hey Marco...well i'm from the netherlands too...
But i'm gonna keep it in english, so the rest can read it also
Those really are the speakers that come from my (Dutch) GTS...
And it really says it's 12W
However...what is the RMS
Wattage that you're amps produce?
Also putting a bit more power on the speakers is better than to less! (i've build some high quality sound systems, so i know what i'm talking about)
But al that has changed since a bought my GTS...now i'm more into tuning
However...try to dissconnect al you're speakers except the rear's and gently raise the volume too it's max,
Then doesn't it make any popping noises?
And to improve you're sound even more, put some damping mats inside the door panel & preferably in the rear (that's what i did)