Using iMac 27" for displaying HDMI output I have an HD satellite box which I previously connected to my old PC.
I am interested in using my new iMac 27" 5K as a monitor for its output.

I did go through the various answers available, but some contradicted others, and many were outdated. Currently, I connected the box's HDMI cable to a Kanex Mini DisplayPort to HDMI adapter and then to the iMac, and as you can guess, it failed to recognize a second display. 

Is there any way around it? Either by some software or a different adapter?

Thank you.
It can't be done. The 5K iMacs only have MiniDisplayPort/Thunderbolt output, not input, because DisplayPort 1.2 can't handle video at 5K resolution and so it couldn't be used to drive the iMac as a display in Target Display Mode in the same way as some other iMac models. The 5K display on the iMac can only be used with the iMac, because it doesn't have any inputs capable of accepting a 5K input from another source.