Huawei echolife HG520b bridge mode

I am trying to set up my old Huawei echolife HG520b into bridge mode to connect to my sky box and xbox. I am trying to set it up to my thompson plusnet router but the only manuals I can find are for a slightly different series and the settings seem to be different and I can only do some things it says when I set it to routing mode rather than bridge mode. If nobody has the answer, is there some other way of doing it? DD-WRT doesn't seem to support it as far as I can see. I NEED HELP ON THIS MATTER AS I AM LOATHE TO DOSH OUT THE CASH ON A SKY CONNECTOR!