In the UK, BMW offered 3 audio levels in the 3 and 4 series platforms. 'Base' Audio with no amplifier, no tweeters and 6" under seat 'woofers', which sounded pretty terrible. 'Hi-Fi' which added tweeters in the front doors, a centre speaker, 8" under seat 'woofers' and an analogue fed amplifier in the boot. And Harmon Kardon, similar to the 'hi-fi' set up but with a more powerful digitally fed amp, and rear tweeters.

 

While the Harman Kardon in these cars isn't 'bad' for a factory system, there is still a huge amount to be gained dynamically and tonally in adding a DSP amp, replacing the cheap factory speakers and adding a dedicated sub to give real sub base.