There are a couple of approaches, analog, Digital to Analog, and Digital to Digital, followed by a DAC. With analog, you can get the output from the headset jack (3.5mm) or from the 30 pin connector. Both in my mind, and based on experience, flakey connections. If you want a solid, gap free, intermittent free, left/right hand balance correct at all times, you want to go digital. In that realm we have:
- Wadia 170i
- Musical Fidelity
- Cambridge Audio
And many others. Which are best? Which are compatible with iPad 1 through iPad 4?