Not sure why but 7z wouldn't extract your files for me either. I could download them and open them but the file list was empty. When I performed a test on the archives using 7z it identified there were files in them however could not extract them as it just showed an error.
I was however able to extract the files using the following software:
Download 7z Extractor
Hope that helps someone else as it did me.
On a side note, Great work on this texture mod. Looks great :)