Your best bet for the car would be to get a receiver than has iPod control built in. This way music selection is controlled by the receiver and not by the iPad. Makes things a lot easier. I have an older Alpine with iPod controls. Haven't used a CD since I bought the iPod cable for about $50. That was the first or second generation of iPod control Alpines. The newer ones improved a few things, but its basically the same thing. I highly recommend them. My wife uses a cassette adaptor in her car with her iPod. Far too clunky for me. She doesn't mind it because she only uses it on longer trips, and uses the shuffle feature. If she used it like I do, she'd hate it.
As for home use, there's a camera attachment for the iPad that has USB digital audio output. Connect that to a USB DAC and you're good. Or you can get a Wadia iTransport and a dock extension cable (I've seen them for about $30 or so) to use the iPad. No idea if the iTransport is compatable with the iPad though. I don't own either one. While I'm on that subject, make sure anything you buy is compatable with the iPad. Some things aren't compatable with the iPhone, believe it or not.
As for home use, there's a camera attachment for the iPad that has USB digital audio output. Connect that to a USB DAC and you're good. Or you can get a Wadia iTransport and a dock extension cable (I've seen them for about $30 or so) to use the iPad. No idea if the iTransport is compatable with the iPad though. I don't own either one. While I'm on that subject, make sure anything you buy is compatable with the iPad. Some things aren't compatable with the iPhone, believe it or not.