Hi Doug,
The Sky HD box only has 1 HDMI out which needs to go to the TV.
The box has an optical digital out which carries the 5.1 surround channels.
The usual way would be to run cable from the Sky box directly to the surround sound amp.
The picture goes to the TV via HDMI, and the sound goes to the s/s amp.
You will have to select the sound source on the s/s box to match the input (usually AUX or something like that), but it should do the trick.
If the DVD player doesn't have an optical input, you may need to use RCA phono connection from SKY > DVD, but this will only be stereo rather than s/s.
Charlie