Here is quick, cheap, and hopefully warranty safe solution - adding stock tweeters.
My 2009 X5 also came with base audio - something I didn't expect with Prof Navi, USB connect and SAT. I have one more year of warranty so we will wait before any major changes and BSW stage one is definitely my first contender.
It was a pure accident that I noticed blue plugs behind the door panels when my car was tinted at the shop. Exactly the same plugs that are used to connect stock tweeters. By adding them you would technically follow the same scheme that BSW uses when connects their front tweeter to mid-range speaker. You can order two tweeters from the dealer, they cost around $30 per piece and installation should take no longer than 30min.
Since I had my treble settings at high to get max out of mid-range, at first I got a lot of noise but after playing with the audio set up for a while I got comfortable sound that I like quite a bit. It certainly is not perfect (my old E53 had top hi-fi) but I like it even better than my wife's hi-fi in 328. In my opinion sub's were already producing good enough low's, what I was missing are highs and hated that feeling that the sound (especially during talk shows) is coming like from a box - adding tweeters for me fixed it and I am quite satisfied with the result taking into account cost and level of efforts.
If anyone is interested BSW has very good video on how to disassemble door panels here (
Part 1: X5/X6 (E70/E71) 2007+ Stage I Speaker Upgrade Install - YouTube).
Note that my X5 was manufactured in 08/2009 and according to BMW Product Content Changes document here: (
http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja) hi-fi should have been standard audio equipment up to 10/2009 so there is no guarantee that all X’s with base audio would have presets for tweeters but even if not, the way the system is set up - mid range speaker had two connectors, one for wire that carriers signal from the head unit and the second one for a cable that runs to the top corner of the door panel where it suppose to connect to the wire from the tweeter (through blue plug) - you can see all this in the BSW video referenced above. So you should have no problems getting the connecting wire from a dealer if it is missing and retrofit the whole thing.
Again this is just marginal improvement in the sound quality but in my opinion well worth 60 bucks.