Yea first step is to sound deaden the whole entire car. Then upgrade the stereo or you will be just chasing your tail.
Speaking of which who wants to help me tear out the interior of my new 2012 Mazda to sound deaden it.

 

I too tried the Boston SE-85's and I ended up returning them to Crutchfield. They didn't have the same amount of bass impact that the OE speakers did, despite the fact that they had a much larger magnet and claimed a high efficiency level. I think we're pretty much stuck with the OE speakers unless you're willing to replace the whole head unit (I'm not).

I'd had such a wonderful experience with a past set of Boston Acoustics Ralleye series components (that were amplified) that I wanted to get that sound in my wife's Mazda 5, but looks like it is going to be harder than I expected.

Also, other bummer is the stupid thin plastic door clips that shatter when you try to remove them. Mazda now says that they are a 1 time use clip and you should just buy replacement ones any time you take the panel off. Not real convenient. I ended up nursing them out, but still broke 3 of 10.

 

mdashi: I just installed the BA SE85s.
I found that though I dont have any more bass than before, the bass I do have is cleaner and less muddy.
I am able to play the stereo louder before it begins to distort.

For my $90 for all 4 speakers, I am happy with it, but, I am considering a powered underseat sub as a next step to give me fuller range bass.

Dom

 

I am considering getting the Metra 95-7521B for DDIN radios for my 2012 M5. Unfortunately Crutch field does not (as of this post date) carry this nor does Car Toys (local car stereo install chain) I am reluctant to risk buying and doing it myself without seeing a more experienced/pro installer have some success.
Any one have any advice?