hmmm... Well, I don't have a changer installed, but I did an extra line-in to my system, and originally we tried the $20 line-in adapter, but because of the Sirius tuner box it didn't work and I had to get a more complicated line-in adapter. I don't know if this what your situation calls for though.
I would call Kenwood support or Sirius Support, that's what we did when it didn't work with the line-in adapter. And that's how we found out I needed the more expensive box. Unfortunately it isn't on or is very difficult to find on the kenwood website, and I don't have the model number handy.