Do I need a monoblock or a multichannel car amplifier?

A monoblock (single-channel) amp is built to drive one or more subwoofers and is the most efficient choice for bass. A 4-channel amp powers front and rear speakers, and a 5-channel amp combines four speaker channels plus a dedicated subwoofer channel so you can run a whole system from one chassis. Pick a monoblock if you only want more bass, a 4-channel for door speakers, and a 5-channel if you want one box to do everything.