2-channel amps are designed for two speakers and 4-channel amps for 4 speakers. You can usually bridge a 2-channel to one and a 4-channel to two channels. This will half the impedance of whatever the speakers are.
2 channel can run a left and right speakers=2 pos and 2 neg connections. multi same exept in how many channels it has 2,4,5. mono amp is a sub amp only 1 pos, neg connection. but can have 1+ subs depends on ohms the amp is rated at and ohms of subs
2 seperate amps for sure..... that way you arent restriced to the same frequency... i would go with a 2-channel amp (that has around 300 rms) then i would go with a mono block or a 2-channel amp that pushes at least 1200 watts (600 per channel if its...