Wiring 2 four channel amps but only have 2rca outputs?

I have 1 four channel amp that currently runs a sub and 2 6x9's. Im using up the 2rca outputs on my head unit for that. I only have 2rca outputs on the hu but have bought another 4channel amp which needs to run 4 other speakers at the front. How do i use rca splitters for this jobbie to ensure it all connects properly? I dont know which way to do it? lol