I have just updated the TrainzDEM to version 2.6.5 (x64).
The manual on page 15 mentions ground textures versions 6 and 7. However, these assets are not in the folder mentioned there:

I would be grateful for your help in obtaining them.

Oh, I didn’t notice and I didn’t pay attention to the name of the downloaded file on download page.geophil wrote:You will also have to download and run "Update Ground Textures for T:ANE and TRS2019" from my download page.