T5810 max psu power for gpu?

I've looked up the manual and it states that you can install max up to 225w GPU, however my question is, since there's 1x6 pin and 1x8 pcie power connector aren't those lines separated load wise or they are capped at 225w? and yes I've the 685W PSU

Or at least someone could explain to me why there's so many lanes for power, I know that there's one for, motherboard cpu, sata