your taking the long way around when your extracting as obj and not keeping the textures applied
there's 2 methods that would save you time from re-texturing.
1.) Take the source code for the World Packer (which takes the world LTA and converts to DAT) and reverse it to make a DAT - LTA converter. This would hold textures, spawn points, game start points, triggers etc. and it could be used for hacking
2.) if your doing it for video, rather than making a LTA decompiler, convert the DAT files to the same file format as CS:S