I was going to post that on the web site, you can click the title (Audio Test Files) at the top, and select Download. It will create a ZIP and off you go. But then I tried it and OP is right--it failed.

Ctrl-a will select all the files for downloading in Firefox. That's the only way I could see to grab them all at once.

You will end up receiving three .zip files that unpack to about 5 GB total.

Worked fine for me in desktop Safari... shockingly enough.