Quote: "you can set more than one fullscreen shader"
Yes, the user can set multiple fullscreen shaders and switch through them during the game, but PB doesn't allow multiple fullscreen shaders on the screen at once, too.
If you want to use multiple Fullscreen Shaders you'd have to merge the shaders, there's no other possibility in PB or the Stock version.
Quote: "FPSC 9 doesn't really feature any post processing effect out of the box"
Well, it does actually, it's kickin' since 1.17 and features a Bloom Shader (made by bond1) and a Depth of Field Shader out of the box.
-Doomster