I have 4 original Xbox360 gamepads connected to my PC, and 2 original Sony_DS3 gamepads.
I did a bunch of experiments.

I haven't found a single way to play with more than 5 players. (more on that later)

For connect DualShock3, i used ScpToolkit wuth emulate Xbox360 controllers. Anyway tested with DsHidMini too.

Another game, where support more than 4 gamepads. Works fine! In one game in settings have one checkbox (Xinput - disable for game more than 4 players). In game just needed
uncheck this.

Steam detect all 6 gamepads... i tried run DuckGame with Steam input, without Steam input... Tried install\uninstall custom xbox support driver...


What's most interesting... Duck Game It also sees 6 gamepads. But connected only first 4 gamepads (NOT Player ID), which I started to push any button. It mean, if i start game and push START button or A button on Dualshock3, then start game, connect to local game:
P1: DS3, P2: XBOX360, P3: XBOX360, P4: XBOX360... Another one DS3 and XBOX360 gamepads don't react at all. Even if you turn off all DS3, last XBOX360 no any reaction...

If restart game, you now can use any you want first 4 gamepads for controll...

About 5 playrs... I find one way, how i can play with 5 playrs (DuckGame see and have reaction on 5 gamepads... It DsHidMini when DS3 connected with Dinput mode... But work only 5 gamepads).