No way to bypass the DAC and get a SPDIF or Toslink signal to send to an outboard DAC. Most folks actually don't think that the iPod DAC is all that crappy.
To get the most out of your iPod you should be ripping Apple Lossless or .wav.
And instead of using the headphone out, get a high grade cable that comes out of the docking port to your preamp - this is a fixed level line out signal that is not attenuated by the iPod volume control. it is a more complex cable to build, and its more delicate (especially for on the go use) but it sounds much better.
To get the most out of your iPod you should be ripping Apple Lossless or .wav.
And instead of using the headphone out, get a high grade cable that comes out of the docking port to your preamp - this is a fixed level line out signal that is not attenuated by the iPod volume control. it is a more complex cable to build, and its more delicate (especially for on the go use) but it sounds much better.