quote I assume some menu option to make the output from the STB on a different channel/frequency (forgive the terminology i don't know)
Yes this is possible and you can also adjust the level the signal comes out of the box to serve more than one TV, and also the sound output level in the diagnostics.When you have your install done the technicians do not normally connect up more than one TV via a single digi box
as this is could be in breach of their sky contract .