Aftermarket Fuel System, Single or Dual Feed?

i'm looking into an aftermarket fuel system, and i came across one that i would like to get. but they sell a Single feed -10 thats rated up to 750 hp & A Dual Feed -6 thats rated up tp 950hp

but i'm wondering if on a dual feed system, does each fuel rail get a hose and there is no return line? or do both lines go to like a Y block and then to one rail then to the other and then to the return?

i know nothing of fuel systems, especially of aftermarket ones for high hp applications. any info would be great.

thanks
joe