You definitely don't need the first one, it's a mono amp, hence it only has 1 channel. To be honest, I'd recommend using a separate amp for the sub than you use for the other speakers. But, if you are intent on using only 1 amp, it is possible to use a 4 channel amp if you do the impedence right.
"I'm not driving too fast...just flying too low"
-03 SB Cobra vert- 2552 of 5082 Born 02/25/03
90 7up vert - new project-07 DSG Focus -DD