Audiophile Play with an iPad
iPad as USB Source
Back in the early days of the original iPad, it was discovered that Apple's Camera Connection Kit (hereafter referred to as the CCK) would allow the iPad to interface with certain USB DACs. There were all sorts of limitations involved and the list of compatible DACs was relatively small, but it was still a novel way to use the device --- bypassing the decent but still decidedly consumer-grade internal DAC, the iPad could be paired with a much higher quality dedicated unit.
Fast forward a few years and things are looking better. The iPad (and iPad 2 obviously) with current iOS and a CCK will pair with many USB DACs, though still not all of them. And the prior sample rate limitation of 48kHz has been removed --- you can easily play 24-bit/96kHz audio, and I've heard unconfirmed reports of up to 24-bit/192kHz with certain gear. Here's a thread discussing hi-res audio playback on the iPad.
What's required: The basic setup is just an iPad of any type and the CCK. This should interface with most DACs that have a standard USB 1.1 input. Certain DACs will require a powered USB hub to be added to the chain. Some USB implementations seem to confuse the iPad, making it think that too much power is being drawn, even if the DAC has its own AC power. See this link for a list of compatible DACs.
So what are the benefits? At $29, this is by far the cheapest way to extract a digital signal from the device. Most of the dedicated "digital dock" type devices on the market are designed for iPods/iPhones and don't have room for the big iPad. They generally cost a lot too. The camera kit is a cheap way to add an extra bit of functionality. One could pair it with a portable amp/DAC unit such as the HeadAmp Pico USB DAC/amp and have a very nice transportable setup, or else use it as a source in a larger home system. As seen in the picture, I'm using mine with a Kao Audio UD2C-HP integrated DAC/amp and Denon D5000 headphones. The whole rig is small enough to fit on a nightstand, and it sounds excellent.
The Home Sharing feature in iTunes also extends to iPads, which means even a basic 16GB model can have access to a massive library of music. This essentially transforms the iPad into a network streaming audio transport. I've used it to play 24/96 and 24/88.2 hi-res tracks and it works great as long as your network is up to the task.
iTunes not really your thing? No problem. You can use one of several different apps to enable the iPad to play FLAC files. Golden Ear and the cleverly titled FLAC Player are both audiophile-oriented apps that accomplish the goal. Another option is the free OPlayer Lite. It's a do-it-all program that is not strictly audio-centric, but nonetheless works well for FLAC. And the price is certainly right.
At $29 you really can't go wrong with the CCK. There are other methods of getting a digital output from the iPad but none are so cheap or have such a low profile. In the event of your DAC being completely incompatible, you could at least still use it as intended to import pictures from a camera. It's a non-audio related function but surprisingly useful in some cases.