OP check the settings menu for the Topfield and see if you can set the resolution output. At SD quality There won't be much between your scart or HDMI. IF your box will do 1080 or 720 then disconnect the scart as it may not allow upscaling if scart connected...highly unlikely but check just in case.
Paul
Onkyo 875, Monitor Audio RX6 GW,Monitor audio RX centre GW,Monitor Audio BFX rears, REL QUAKE,Arcam CD73t CD ,Russ Andrews Yello mains cabling & PBJ interconnects,Sterling Black Mamba speaker cable.