You don't need a full VPN to access your Humax remotely - you only need to forward the ports that are of interest, typically 23 (telnet) and 80 (http). I wouldn't bother trying to forward 21(ftp) due to the slow speeds you would get.
This is best done using PuTTY. You need to port forward from your router to the ssh service (22) on the Humax and then set up a tunnel under the PuTTY SSH settings. First, get SSH working remotely, then add a local tunnel to 127.0.0.1, from port 80 to port 80 and save the config. Close your PuTTY session and restart it and then point your browser to
http://127.0.0.1 and you should see the WebIF. It's surprisingly straightforward once you have done it a couple of times. You don't need to bother with SSL either because the SSH session is already encrypted. If you want to do the same with telnet, then make sure that the ports are 23 at either end of the tunnel and then telnet to 127.0.0.1 (windows systems don't normally have telnet open so that should be fine).
What you are doing with this setup is you are telling your computer to echo the service that is at the other end and to make it appear like it is actually running on your machine.
Once you are happy with the basics of SSH, you should do 2 more things:
1) Change the port to something that isn't guessable, because hackers go looking for open SSH services
2) Disable keyboard authentication and use keys instead, even if a hacker or 'bot finds the port, they're not going to get in unless they are really lucky (the odds of winning the UK and euro lotteries on the same week are probably more likely)