Hope I am not beating a dead horse by resurrecting this one. The way I understand it, if you were to amp the BSW upgrade you would need to install a crossover network. Most crossovers will give you a 2 way setup (mid and tweeter). There should not be any "gap" in the frequency response b/c your mid will handle up to 3500 Hz (or so) and the tweeter takes everything higher. That being said, you have a 5.25 in the door panel (low and aimed downward) and a tweeter in the sail panel. This represents "off-axis" mounting. This may result in some odd reproduction.

I would like to see an ampable three way set up utilizing the 2.5" mid. Send sub 800 Hz to the doors, 800 to 5000 to the mids, and everything higher to the tweets. This would essentially recreate the stock setup but with more power and better drivers. This should raise the soundstage to where it needs to be. However, everything I have read recommends against placing speakers on the dash. I would like to think that the engineers that designed our vehicle chose the dash location for a good reason. Other than just because they fit nicely on the dash.

I can say this, my wife's bone stock system in her 325xi beats the snot out of mine. The 325 has both mids in the doors and tweeters in the sail panels. I believe this provides better imaging.

Halston, care to tell us the specs on the BSW mid? I.e. power handling and frequency range?

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2004 BMW X5 3.0i - Mine
2011 BMW 328i xDrive - Hers
2002 BMW 325xi - waiting for a new owner