My 1st thought was "How, the dumb SSH server on QNAP hardwires 'admin'" (in the past I tried all sorts of thing, really don't want to be SSHing as "root" , but it's just hardwired)
Looking at the QNAP site:
So pretty much, you can't disable "admin" if you want to be able to access the NAS.There are two reasons for not disabling the default admin account. If you want to access the QNAP turbo NAS via Secure Shell (SSH) or Telnet, do not disable the default admin account. Also, if you're going to access Console Management, do not disable the default admin account.
The obvious "fix" is for QNAP to install a regular sshd and telnetd , so we can do as they "suggest" (but the rule out)