Most people with aftermarket cd players dont need the itrip. All you need is a $8 rca cord that plugs into your ipod or whatever mp3 player you have. That is if your stereo has RCA inputs. Which many do.
I have an alpine unit, so i had to buy a $25 cord that converted the AI-Net input to RCA. Some people are saying they had to buy the big box that alpine sells. Not true. They tried to get me on that. All you need is the cord.
The sound quality is exactly like you're listening to your ipod w/headphones. No radio interference to deal with.