I understand that you are having some issues in order to control a set top box (Humax) which is not included on the supported devices list.
Since you have not included the specific model number, I recommend you to test first all the available Humax codes. If you are still having issues, I recommend you to check the following thread, provided by alanrichey42.
The HD box is branded as "OSN HD Box" No model number is mentioned on it. After some google research i found out Humax is making the decoders for Orbit/Showtime. I've tried all the Humax codes but unfortunately with no luck. It seems I have to create my own remote. So far there's nobody in the forum who's using the same HD box and found a solution.
I can't help much either as OSN is not a recognised manufacturer on the Logitech Harmony database so I cannot install it on my Universal Remote and check the codes.
Have you tried the Humax Custom Remotes on the JP1 forum ?
If you do manage to learn any buttons using http://remotes.slingbox.com I can probably analyse the myRemote.lrz file (Use the Export Remote option) and determine which remote would work.