I'd say two, one for the speakers and one for the subs. I'm running an ancient Jensen 208W amp powering two alpine type-Rs and a 300W Dual powering two 12" Pioneers behind the seat. Haven't really got to run the subs under full power yet, need to strap down the box better before I can do that

.
__________________
1970 Chevrolet C-10 w/355sbc

2010 Silverado Daily Driver

1971 Mercedes 280sl project car