megaman8x wrote:map packs like nightmare house or outpost 16
those are mod's
but depending on mod, it should be possible to play them on OC, but in some cases (or all) you need to decompile the maps of that mod and fix/change/modify some parts to make it playable with multiple people, iirc.
put the .bsp file in the obsidian/maps folder, maybe you'll need some files from materials models and sound folder too, depends on if they bspzipped the needed stuff or put it globally into the mod folder