The reason for the advice to connect using the component cables is to minimise problems caused by HDCP (Google it). If your Humax box does not have a component output (very common these days), then it is unlikely you can stream protected content. Although it is worth a try using the HDMI from the box to the Slingbox and then HDMI from the Slingbox to the TV.
Otherwise you are forced to use an SD source for the Slingbox. You don't say what the video connector is, but if it is the standard yellow RCA plug (with the audio being Red/White) then use that. Otherwise you will need to buy a SCART to composite converter as with your other box.
Thank you for your response, I think your right, I did think I would need a converter, that's OK its what I'm using ish on my Solo. I probably didn't need a 350 another solo would have done the job, as I will bewatching whats on my box ie recorded, or live in SD. The outs that are on my Humax the Video, Yellow, and the Audio, red white, If that would be ok to use.