this is going to be a dual mod with a Cuthulu PS3 PCB and Madcatz Retrostick. Dual Mods needs common ground for all signals. Those both friends fullfil this needs. When dual modding the Cuthulu has one big advantage: Extra Connector for the xbox360 signals.
Take a deeper look at the pics. Here`s just the connection between ps3 pcb and xbox360 pcb wired.
It's a really good design.