Just finished the cable. I am using a V1 E250 with the latest beta firmware. The cable has line level audio out when 5vdc is applied. I used a female 1/8" stereo jack due to the connector that I had in the vehicle already and for power I have a cigarette to usb adapter. Got the dock connector from mouser http://www.mouser.com/search/Product...656-DD1P030MA1
and used the pinout provided by rox. It works great. Sound quality is perfect with no noise. The sansa charges perfectly and the usb still allows for data transfers.
The dock connectors pins are easy to bend. Use very small gauge wire and use a good magnifier and iron.