Good suggestions.

Also see if you notice the distortion when the empeg is plugged into your stereo (or through your computer's line-in). If the distortion disappears in that case, then you might be looking at a problem with your car amplifier, speakers, or wiring, unrelated to the empeg.

Another thing to consider is that the Kenwood deck's line inputs might be rated at only 1v, and the empeg's in-car outputs are 4v. In that case you might need to significantly reduce the empeg's output volume before the distortion disappears.