I've never downloaded the "big zip file", which isn't an officially supported Orbiter installation archive, so I can't help you much, but like Nicholas Kang stated, the target texture directories should be the same as they are in "Optional texture packs" official downloads.
If they are however different, the Textures2 is simply a directory which takes precedence over Textures when files with the same names are present in both of them. High resolution textures would be read by Orbiter whether you put them in Textures or in Textures2, but if you put texture files named the same for an object in both Textures2 and in Textures, the textures from Textures2 will be used in such case.
What files/directories are inside the "Textures_Orbiter_2012_100830" subdirectory from your screenshot?