Hi there,

For sega genesis try the things written here:

How do I enable 4 player games (multitap) for sega genesis

But as you follow the link i posted in there, it is not possible to make psx 4 players work, as there is no emulation for the psx multitap.

Every station that worked out of the box with 4 players (like n64) works without the need of configuring anything. Just start the emulator with your controllers plugged in and start gaming ;-)