It was only after the wife had me comparing Freeview E4 and H2S E4, i admitted there was a massive difference in quality. Seems the zGemma boxes have their outputs configured considerably differently to any other box you might plug into your TV, and there are no settings to change them.
I instead tweaked some of the TV settings (contrast, brightness, sharpness, Dynamic contrast, colour, etc.) and it looks loads better now.