Attach a speed sensor to the serial port to give speed dependent volume.

Definitely a good idea - a lot of cars these days have already got an electronic speed pulse generator fitted for cruise control, electronic speedo, engine management, ABS, etc. If anyone at Empeg needs any more info on this, drop me a mail or give me a call at work anytime and I'll try and give you a few pointers how to go about finding the right cable in various cars, etc.

Dominic

Cambridge Car Audio
http://www.cambscaraudio.co.uk