I also read the review that said the standard stereo was very good, which is why I was surprised that I really didn't like it. I tested it thoroughly before and during my test drives. The bottom end was too boomy, the mid range lacked a little clarity, the high end was a tad harsh. Perhaps the worst thing for me was the sound stage it produced. I noticed that all the sound seemed to come from an area around my legs. There are door mounted tweeters with the base stereo, but the dash-mounted center speaker of the HK should alleviate the staging issues. I have not heard the HK to verify that it solves these problems, but I ordered it anyway. What I know for sure is that I wouldn't have been happy with the base stereo. Then again, I'm a musician and am pretty picky about sound systems. Your mileage may vary.
2013 X1 35 MB/Black/ULT/CW/HK/Lighting/Paddles
2009 335i xDrive Coupe Black/SB MT/SP/PP/CWP/PDC/Logic7/iPod
2004 325iT SB/Black SP/PP/CWP/PDC/HK/Step/Xenon
2006 X3 SG/Black PP/CWP/Xenon
2006 330i SG/Terra MT/SP/PP/HS/CA
2004 330i SG/Black MT/SP/PP/HS (my
2001 325i SG/Black MT/SP/PP/SF/Xenon