Raspberry Pi 2 no DD or DTS

hi, looking for a bit of a steer..

I just got a Raspberry Pi 2, installed the latest OpenELEC/Kodi on it, wireless Logitech keyboard, wired Ethernet, HDMI cable to my Sony STR-DA1200ES and HDMI from the Sony to my TV.

Everything worked as expected Except no DD or DTS on movie output.
I've enabled audio passthrough on the Pi but I just get a loud click when a movie with say DTS sound starts, then no sound at all. When I disable audio passthrough I just get sound through the TV speakers.....but not what I'm looking for!

Am I missing something obvious here ?

The amp and TV are probably 6/7 years old now,

It's like the amp is routing the picture correctly but not decoding the digital audio

Any ideas ?

Rgds
Aidoaidan