There is a kit from Alpine -- basically a retrofit kit... but it doesn't fit our e70s.

You can recode your system to have less signal processing by coding it as the HiFi system as opposed to the base system, but I'm not positive it removes all of the DSP.

I've talked to some installers and done some research and your best bet is to upgrade your front door speakers with a nice set of component speakers (this will add a tweeter to the empty spot in the front doors). Leave the rear door mids alone. Upgrade the subwoofers with a nice set of SWS-8 earthquakes -- these drop right in the shallow opening under the seats. Get a digital signal processor like the Rockford 3Sixty.3 -- with this you can reverse any signal processing then send the signals to an amp. Pick up a nice 5 or 6 channel amp and use that to power your new components, the subs, and the rear mids.

There is no sense in upgrading the sound behind you or even adding more speakers behind you. You want your 'stage' in front of you ad adding speakers behind you just makes it harder to balance the system. With an amp your system will be LOUD enough so, again, adding more speakers isn't helping.

One thing that helped me realize that MORE is NOT better was that I had to be reminded -- 99% of the music we listen to in our cars is in STEREO. It's not like our home theater system which are recorded in surround sound. Your CDs and MP3s have two channels -- LEFT and RIGHT. Adding speakers behind you doesn't change this. You want your music to sound right in front of you so why add speakers anywhere else except to your sides (and possibly a front center channel)? Spend your money up front.

Hope that helps!