My E36 M3 had the H/K premium sound system and sounded like crap in just about the same way that the X5 sounds. Poor bass, muffled sound, not clear or very detailed, the sound has no volume (doesn't fill the car) and is not well balanced.

I upgraded the head unit with an Alpine CDA-7894 (with pre-amp) and the sound quality improvement was simply amazing, I wouldn't need anything better. Cost of the upgrade $200.

Now regarding the X5, it looks like it's not that easy. The first thing I found out is that a speaker upgrade would help. But in the M3 scenario the poor sound wasn't due to the quality of the speakers but to the poor head unit, isn't it the same in the X5?

I really would hate throwing $500 on speakers and still have a level of unclear, busy sound where the lows, mids and highs all seem to interfere with each other. Or are the M3 speakers that much better than the M5, and the X5 unit better than the M3's?

EDIT: I just found the following quote browing through threads, which would explain some of my comments above; "I agree with the general consensus that the bottleneck in our audio systems (at least he non-DSP systems) is *MOSTLY* the speakers, and not so much the head unit."