Pretty sure those people don't know what they're talking about. "Preserving the digital signal" doesn't make any sense. It has to be converted to analog at some point before it hits the speakers, 6' of cord makes no difference. Using a better external DAC could or escaping electronics noise in the iPhone could possibly, but most posters I've read seem to believe that moving the DAC to included Apple headphones rather than in the iPhone will make some big difference. It won't make a difference in headphones that cost a couple bucks to make.
Also, pretty sure the adapter cable will have a DAC since the lightning to 30pin adapter has one to feed the analog pins. Also pretty sure the dock with analog out has a DAC.
As far as needing one in a car. If you've been looking for a single wire charge/ analog audio Y cable like me, you've spent the better part of 5 years looking for one. They don't exist except a $100 BMW cable that essentially combines the Lightning to 30pin and a 30pin to USB and analog mini Y. I've been using a $5 imported 30pin to USB/audio Y with the Apple 30pin to lighting to accomplish this for years, but it's clunky. As is using a lightning extension to move the 30pin adapter to move the adapter further from the phone. I ended up cutting a small hole in my dash near my iPhone mount with the end of the 30pin adapter poking out. Works great, but I'd still like a single wire solution from Apple or anyone else. Why not use a Bluetooth adapter? I'm already plugging a cable in to charge, why not get the best audio at the same time.
If someone has evidence that you can get analog audio from the lighting port without a DAC, please enlighten me because I see no evedence of cable anywhere that would take advantage of it.