First I needed to find out if I could find a plug that would fit. It looks like a typical four pin 2x2 molex adapter. I went to a few electronic shops (Radio Shack, Fry's) and they had every type of molex connector except for that one. I had an adapter that came with a video card of mine that had this type of connector, so I just chopped off the end that I didn't need. Most power supplies have this, as well. The only issue I've found with these is that the clip that insures the cable will not come off doesn't fit very well with plug that's on the amp, so I just snipped it off.
I wasn't able to find the exact pin out for the plug online, and eventually determined the top left and bottom right pings were the negative lines, and the top right and bottom left were the positive ones using a multimeter. It turns out the top two pins are for the left audio channel, and the bottom two are for the right channel.
While I was at Radio Shack, I picked up some "Solder-Type Phono Jacks" (part 274-0337).
The next step was to strip a bit of the wire tips off, slide part of the phono jack casing down the wires BEFORE soldering, and then soldered the corresponding wires to the right spots. On phono jacks, the inside is positive (the little tiny metal part) and the outside is the negative (the long metal part). I decided to do the left audio channel first and used the black jack (black or white is usually the left channel), and then used the red jack for the right channel (they both start with R!).
Once that was done, it was time to plug it up to the amp.
...and then attach the audio source.
And that's it.
