wet sounds ws420 /i pod

I just installed a WS 420 Wet Sounds EQ and it is great. I just have one question regarding it. Whenever I have my ipod hooked up to the system, it is not as loud as the XM Radio or a CD in the cd player. It plays at about 1/2 the volume unlike the radio or cd. I have checked all of the settings on the ipod and it doesn't seem to make any difference. I'm wondering if it's because the ipod doesn't have enough output? I know the XM and the cd's get powered by the deck, and the ipod plugs directly in to the WS 420. Any help is appreciated!!