Those $20 docks are analog out - they use the horrible DAC from the iPod. The digital out docks allow processing by the DAC in your pre-pro or by an outboard DAC. Wadia was the first to market such a dock. The current models are the 170i and the 171i. They aren't cheap. Believe it or not, you can get CD like sound out of an iPod or iPhone using these digital out devices. http://www.wadia.com/products/transports/