Ok so im looking to either the alpine iva-d310 or the iva-d900. Now these head units both come with a brain. Is that needed to wire up your speakers to it?!?!? or does the head unit have the speaker wires and ground and all that in it itself? I guess what i don't get is is the brain an absolute need or is it just for upgrades like dvd playing and other add ons that they have. Can I get some help please!?!!?