If you call Crutchfield, they can tell you what you need. That's what I did.
My ipod didn't provide enough power to run my integrated amp when I plugged directly into it. I had to turn the volume way up to hear anything.
I bought a TEAC HP P50 DAC (also called a headphone amp) from Crutchfield for more power and better sound. You can buy cheaper ones, like the Audioquest Dragonfly. It depends on how much you want to spend and what company you want to buy from. A better DAC has better audio and options. My TEAC came with USB and optical jacks and a hi-def audio software.
Most DACS are portable enough that you can take it wherever you take your ipod. Mine is about the size of the recent WD SSD blue hard drives, though thicker. You can plug it into a laptop or desktop, Mac or PC, and bypass the computer and ipod's audio. The DAC will sound better. The headphones plug into one end of the DAC and the ipod plugs into the other.
I connect my ipod to my integrated amp via a USB cable, with the wide end of cable going into the bottom of the ipod and other end of the cable going into the USB jack of the DAC. Then I connect a cable into the ipod's headphone jack. The other end of that cable splits into a dual for two RCA jacks in the amp.
It's a somewhat clunky solution, but the audio is fine. The next amp I buy will probably have its own USB jack and built in DAC, because most new ones do, meaning I can plug my ipod directly into the amp whenever I want, and I can leave the DAC plugged into my iMac or laptop without having to shuffle it back and forth between my computers and my stereo system.
