Honestly, I would like the system 11 multi just to switch between different versions of Tekken 2 or Soul Edge on one board. Very useless to many but would be nice to see :)
There’s no manual but to answer your other question https://www.arcade-projects.com/threads/retail-cex-playstation-3-to-a-replacement-namco-system-357-369-gex-arcade-board-possible.27006/
The 369 however has an overclocked RSX GPU and VRAM, the normal 357s are more or less the same as regular...