Hi Holger,
the legacy installer uses the same url to download the Linux binaries of Roon Server Legacy as the easy installer script for a generic linux install.
It seems this file does not exist anymore on the roonlabs webspace:
https://download.roonlabs.net/builds/production1x/RoonServerLegacy_linuxx64.tar.bz2
maybe @support can take a look and check on their end what happened to Roon Server Legacy for linux on their webspace?