Audiobug

Hello, I'm sure this question has been asked before but I can't seem to find the answer. I am running an IMac (snow leopard), into a Little Dot Dac_1 via USB, then into my Cambridge Audio AR-30 amp and finally through my Mordaunt Short speakers. My question is this; What levels should all of my volume controls be set at for best sound and safety for my speakers. iMac volume, iTunes volume and amp volume.Any help appreciated.