Looking for DAC to improve sound quality from iPod

I am using and adcom amp GFA 5400 and adcom preamp GTP 450 speakers Paradigm studio 60. iPod is connected with apple doc with analog out. I am also using adcom CD player GCD-600. Had adcom gear for long time all is in good working condition.I get Pandora Internet music from my DVD player. Would like to get DAC to hook up all three components. I have been looking at different DAC on line not sure how the iPod connects to them without using some kind of dedicated docking system like the Cambridge iD 100 or Arcam rSeries drDock or Peachtree iDac. I am new to all this and trying to upgrade without changing what I have. I feel a decent DAC would help.