Howdy,
I'm happy to announce that I have added support for the Terastation II Pro (TS-HTGL/TS-RHTGL) and Terastation III (TS-XL, TS-WXL and TS-RXL) to my Debian Installer project. Debian Stretch and Debian Buster can now be installed on these devices using a modified version of the Debian installer custom kernel image.
All the installer files and documentation can be found on my github page:
https://github.com/1000001101000/Debian_on_Buffalo