You'll get a very low signal...most amps are made to accept 3 volt inputs (or higher)...your average laptop is going to only put out 800 millivolt peak to peak using the headphone or line outputs. Use a preamp and you won't have a problem though. You are also going to have a problem with the signals overlapping if you ever have the stereo and laptop on at the same time using that configuration. I would wire a switch in too swap between the two. If you ever have a line surge from your stereo it could fry your laptop. Just my two cents. rather safe than sorry.