If i connect coaxial digital audio lead to coaxial digital output on sky hd box and audio input on home cinema?

Note your receiver may have Digital Coax out but that does not mean that you will have 5.1 capability. You need to look for the Dolby Digital label on it.( Or check the manual) You will need to check your settings in both the Sky receiver as well as the surround receiver. Also you will only get 5.1 if all the above is true and they are broadcasting in 5.1. Provide model numbers to be sure or check your manuals.

if you have a coaxial out put on it, just run a rca from it to the input of your receiver and your receiver should put it in 5.1. coaxial is just the older version of optical.