The door speakers are (loosely using the term) woofers only (they are just 5.25" drivers in a tuned port). There is cutoff built into the 4x40 amp (not sure at what freq exactly) which only sends low freq to the drivers in the door. They are driven (from the amp) by combining the signal for the front and rear channels. Therefore, if you fade completely to either the front or the rear, they will get no signal. Lots of info here doing a search on how to effectively upgrade the Boxster's sound system including:
-adding rear speakers (to the parcel shelf above motor)
-replacing dash speakers w/ quality coaxial speakers (or even components)
-upgrading the door speakers to 6.5" or 6.75" drivers
Hybrid Mode
