10A * 13.8v = 138w output
Now, assuming your stereo *actually* puts out 1000w, even with 100% efficency, its going to draw 72 amps @ 13.8v
lets say its running at 75% efficency. (eg. 1250W consumed for 1000W output)
that would mean you need ~100A to power the sh!t.
lucky for you, most stereo manufacturers lie through their teeth (for ex, how many "1000W" amps do you see, with 12ga wire coming out (to V+)? no way that 12Ga can handle the actual 100A+ req'd
of course there are legitimate amps that can actually put out 1000W RMS or whatever, but its not going to be free...