I´ve got 2 amps for my subs,but only one.... I´ve got 2 amps for my subs,but only one

Question

I´ve got 2 amps for my subs,but only one pre-out from HU of course.i know i should be using amp´s line out to connect the other one,but it is unable to send unfiltered signal from it,so i´m using Y-splitter to feed both of them and it seems to be fine(is it).But when i think about it,are these 4volts getting to BOTH amps line-in or are they divided,so i´m getting only 2volts each?