This thread is a quick summation of a temporary upgrade I did to satisfy my desire for better sound in my 2008 Mini. I intend to to do a major ( 2k$ ) DIY upgrade as time permits, but I am generally happy with the results of this real easy modification.

First, I replaced the 4" paper cone "tweeters" in the door pods with a pair of economically priced decent quality 1" dome tweeters ( Vifa D26TG-05-06 ) that I've had new in boxes, stored in the garage for a couple of years, just waiting for a project like this. I put a 7.5uf Solen capacitor in series with each tweeter to create a 1st order high-pass filter with a crossover frequency of approx. 3500hz ( these particular Vifa's are a bit unusual @ 6ohm impedance. Depending on the drivers someone uses, the value of the crossover components will vary of course ).
I hot-glued the tweeters into place, and filled the gaps in the door's plastic structural frame around the tweeter's flange with closed cell foam scraps, also hot-glued into place.

I left the OEM mids stock.

I did the front/back wiring @ connector X9331 swap https://www.northamericanmotoring.co...d.php?t=151132, and put 6.8mH inductors in series with the rear 6x9 speakers to give them a lo-pass crossover point of approx. 95hz., so that they would act as pseudo sub woofers. I made the rears low-pass because I don't care for full range frequencies coming from the rear stage. Be careful if you choose to do this as the OEM head unit's low power will not drive low frequencies very loud without clipping. The small amount of dB I have them dialed in at via the stereo's fader is subtle and makes good use of the 6x9's for now. I will disconnect them completely when I install my "real" system.

This is an easy low cost way to get a much better sounding system in your Mini. It ain't perfect.. The high off-angle positions of the driver side speakers ( in relation to the driver's position ) limit the width of the soundstage, the low frequency output is lacking, and the OEM head unit lacks headroom. But it's a good start, and may be good enough for many Mini owners.

Bill in P.G.