As you are fixed on Astra 28E, there's little point in obtaining a CAM for your Humax, as all you will be able to do is use your
Sky card in it to watch the channels on the Humax that you are already subscribed to with your
Sky box - unless that is what you are proposing to do. For this you will need to program the CAM.
The Diablo CAM would be a good choice, as in the future if you decide to add another dish, you will have access to other encrypted channels on various satellites that can currently be opened
A CAS programmer (from Duolabs) will be necessary to program the Diablo - the CAS3+ would be the best version.
Alternatively the Dragon/TRex Cam would be OK (still needs to be programmed, but other programmers will also work with this).
Check the CAM section of this forum for help in programming etc.
Llew