That explains the problem. The 9300-T is a SD only receiver. It has the capability to upscale SD channels. Your HD TV has the same capability, the hdmi connection on a SD box is largely a connection convenience.
To get Terrestrial HD TV with a Humax box you need one of these.
HD FOX T2
HDR FOX T2
DTR-T1000 (Youview spec with Video on Demand backwards epg delivered by an internet connection).
At the current state of the art, look at the HDR FOX T2, if you have a Richer Sounds near you talk to them. They are a cut above the big chains in knowledge., and really competitive pricing.