Found this online in the shield tv forum: Netflix 5.1 sound requires EAC3 pass-through (which SHIELD supports). However, many TVs don’t support EAC3 pass-through (only AC3).
You will get Netflix 5.1 if your TV or your receiver supports EAC3.
Here are the valid HDMI routing options for Netflix 5.1 surround sound:
1) SHIELD > Receiver > TV
In this configuration, the TV does not have to support EAC3 pass-through. However, your receiver needs to support EAC3 decode – most do.
2) SHIELD > TV
In this configuration, the TV will need to support EAC3 pass-through or EAC3 decode via its HDMI input port.