Ok I see. The gamestop controller I used actually is quite good for hacking. It has common ground, and relatively easy to mod triggers (at least compared to some other controllers). One can just remove the pots and replace them with fixed resistors to get the triggers to work as buttons, there is no need for using transistors to get the signalling right.
I'm still thinking about the PS360+, there is a chance I'll still decide to get that instead of a controller.