head unit & speaker wiring
 

So i'm looking to buy a new head unit on crutchfield, but when i put one in my cart it says "you may also want this" http://www.crutchfield.com/p_127SOEM....html?tp=22564
which to me looks like an amp manager, as in the head unit doesnt have any actual power but each individual speaker has it's own amp like the Bose maximas used to do. Is this true? I just disconnected my tailgate speakers, which had their own amp, is this the case with all the speakers? I'm asking because if i have to side step the amps and run new speaker wire to each door that seriously elongates/complicates my head unit install. I'd appreciate any insight from people who have already done aftermarket head units. I've done them before but not in the Disco. Is there a wiring harness out there thats essentially "plug and play"?