HOOKING UP SUBs TO STOCK HEAD UNIT!! CONFUSED!!!?

ok so tonight i am getting subs for my car and hooking them up by myself for the first time. i am just going to hook them up to my stock head unit but i am confused. people are telling me to buy and rca converter that splices into my rear speakers. how exactly does it splice into my rear speakers, and wont that make the sound quality a lot worse. please help!HOOKING UP SUBs TO STOCK HEAD UNIT!! CONFUSED!!!?
the splice is simple the converter has terminals much like a speaker essentially hook it in parrelel... i have a converter and it sounds fine, but it is a newer factory deck that sounded clear before adding the amp. and i have my gains set where i do not overpower the deck causing distortion to be amplified. the "numbers" go upto 35 on the volume, i set my gains with them at 20 and i dont go past that. and the sound is very good. distortion really didn't start till around 25, but i wanted to avoid the built in base curve that it apeared to have, my base tapered off at higher volumes. at 20 it still seamed to be a flat response curve.HOOKING UP SUBs TO STOCK HEAD UNIT!! CONFUSED!!!?
YOU NEED TO HAVE A RED AND WHITE RCA OUT PLUG ON THE BACK OF YOU DECK, FROM THE DECK YOU PLUG THE OTHER END OF THE (RCA) TO YOUR AMP ALONG WITH YOUR BLUE REMOTE WIRE IF YOU DON'T HAVE A PLUG IN YOU NEED TO GET A NEW DECK. I DONT RECOMEND CUTING AND SPLICING IN TO FACTORY STUFF IT COULD CAUSE A FIRE.HOOKING UP SUBs TO STOCK HEAD UNIT!! CONFUSED!!!?
1.) buy and amp/crossover to power the subs

2.) Replace the stock head unit with one that has inputs for the sub woofers.

3) Is it all bass what about the high frequency???????





FYI : hooking up sub woofers to a stock head unit will



a.) under power the subs and they will sound like **** and eventually ruin the drivers.



b) Make the other speaker currently in the car loose power and sound like ****





I suggest saving some money and taking your car to a service center that specialize in car audio.