What exactly does the problem manifest like?

Well, basically, I open the Serious Editor, hit File, go to Open > Document... And then browse to my SteamApps folder then to the The Talos Principle folder then to Content then to Talos and... It doesn't list anything besides the Config and and Scripts folders. When I set it to see all files and try to open a particular .gro file, it just says:

There is no registered document type that can open '$C:/Program Files (x86)/Steam/SteamApps/common/The Talos Principle/Content/Talos/All_02.gro' file.

And yes, I can see the SS3:BFE assets which makes this even more weird.

Wait, you are trying to open Talos assets from within SS3 editor?

Yeah, he mentions the Serious Editor 3.5. If this is the problem, "The Talos Principle Editor" is the one. http://i.imgur.com/PSaCoKZ.png

It cannot work that way. For two reasons:
#1 You would have to open those assets from the Talos editor, and save them to disk. That will extract those particular individual files. Then you _might_ be able to load them in SS3 editor. but....
#2 The file formats are not backwards compatible in most cases, and since SS3 editor is much older, they probably won't open there anyway.

Oh... I just thought the SS3 editor and the Talos Principle editor were pretty much the same thing.

There's about 3 years of development difference between them. :) You can still load SS3 assets into Talos editor (for most part), but not the other way around.
Btw, you might be able to export Talos assets into portable data (textures can be exported into .tga files, models into FBX....) and then import that into SS3 editor.

Sounds good. Thank you so much for the help, everyone! Keep making awesomeness!