The 170i is intended to be connected to a DAC. It does have the option of sending an analog signal to a preamp, similar to the analog output of a CD player. The 170i in the analog mode offers no distinct advantage over using an interconnect from the headphone jack to the preamp, you are still using the internal DAC of the idevice. The beauty of the 170i was its ability to extract the pure digital signal, something Apple did not initially permit. Even a low cost DAC should sound much better than the internal DAC.
