Sub install... no preouts? Options

[slipgun]

I have a JVC headunit that has no preouts I am sad to say *got it with the car* I love the sound of everything, but I want subs and there are no preouts to run into a crossover. Does anyone know how I could filter the other sound comming out into a sub correctly, I am willing to replace my back speakers to run subs if I must I just wana get subs ya know Thanks all

[Guest_Matthew_*]

why not just get a new deck??


i know its the most cost effective (big word day) way but some day you might want to add a 4 channel amp


also if you use the speaker level inputs i hear that if you dont have it grounded perfectly you will hear additional noise in the music.