Never mind - AmiFTP proxy mode works with ftp-proxy from SuSe which also exist in Debian/Ubuntu/etc
In /etc/proxy-suite/ftp-proxy.conf set as follows...
Code:
[-Global-]
AllowMagicUser yes
DestinationAddress localhost
DestinationTransferMode passive
Group nogroup
Port 2121
User nobody
Important here are DestinationTransferMode and AllowMagicUser (which allows proxy connections as AmiFTP likes them - "USER anon@target-address").
Set AmiFTP to use proxy, configure proxy to the linux box and port 2121 (or whatever you chose), and voila
Oh - also set "RUN_DAEMON=yes" in /etc/default/ftp-proxy and enable it with "systemctl enable ftp-proxy.service" and start it with "systemctl start ftp-proxy.service" (or "restart"), a process listing should show "/usr/sbin/ftp-proxy -d" running as nobody.