I had same problem in one of my old cars with a big stereo
Pull the stereo out - This will fix it
If you don`t want to do this then it might be easier to put bigger alternator in like i did
Car stereo`s draw a LOT of power from your battery, if the alternator can not keep up with the current being drawn then you`ll end up with flat battery (eventually)
My car used to stall when taking off from traffic lights if i wasn`t careful and then i`d need someone with jumperleads to come and get me going again
After i put new alternator in there was no problems