This upgrade is so good that I felt inclined to share my views on it despite my initial scepticism! My car has the Harmon Kardon factory fit speakers/mini sub and had been previously upgraded by Baris with his stage 1 amp upgrade, which whilst very good the improvements are quite subtle over the standard HK set up. (I believe non HK equipped cars benefit more from the stage 1 due to how poor they are to begin with!!!) I've covered several 100s of miles in the car since fitting the stage 2 upgrade so I have spent hours in the car with a multitude of music styles to go through on the iPod/Intravee. First impressions are quite surprising. What's immediately apparent is how much louder the system sounds from the off. Less clicks of the volume knob are required to reach a much higher volume. Bass is much more evident at lower volumes and feels not only punchier but deeper too. This was proved when I listened to some late 90's ambient Drum & Bass from LTJ Bukem mixes and Big Bud and the like. These are tracks that I simply couldn't or wouldn't listen to in the M3 as the bass simply wasn't there to make such music enjoyable so it was nice to actually enjoy this trip down memory lane whilst driving the M3! Don't expect earth shattering window rattling bass, but none the less the lower frequencies can be heard and are satisfying enough! As for the higher frequencies, it's not massively different however I no longer need to have the treble turned up to maximum to hear the crisp trebles of the music allowing that extra bit of adjustment on lower quality tracks that need the additional range. I found myself trying all sorts of different music from rock, to R&B, hip hop and dance music and I was not disappointed with any of the genres I tested it on. The Weeknd's Trilogy sounds absolutely fantastic for example! This is an extremely worthy upgrade and has made the system sound more akin to that of a more modern car than one 10 years old - I would almost go so far as saying it is better than the system in my e90 330i (which had the logic 7 underseat subs). So whilst this will never be a substitute for a bespoke system with aftermarket amps/subs filling the boot or mega expensive speakers to replace the factory items it is a fantastically cheap way of getting some much improved quality sounds in your M3 that will even fool your friends at modest volumes! In a nutshell this will breathe some modern life into your BM54 set up and is well worth the small outlay. This is the kind of sound quality a top of the range BMW M such as the e46 M3 car SHOULD have had from the factory. Highly recommended. You won't be disappointed.