It's possible that you have the wrong type of HDMI cable. You need one that has Audio Return if you want to feed your Home Theater system with audio from the TV. There are several types of HDMI cable,some with audio return and some without. The two basic types (not including Ethernet) are described below - you need the High Speed version, which does have Audio Return.
HDMI Standard This
is the most basic HDMI standard which all cables have to meet. Cable
should contain all the connections required for HD transmission, and
have to deliver at least a resolution of 720p, (Video mode of 1280 x 720
meaning 720 Horizontal lines). These cables do not contain an Ethernet
connection, or audio return.
HDMI High Speed HDMI
High Speed cables will support higher resolutions of 1080p. This means
at least 1080 Horizontal lines, and cables rated at this specification
may well support high resolutions of up to 4096 x 2160 (2160 Horizontal
lines), check individual cables specifications for this data. Cables in
this specification will also support a data transfer speed of 10.2Gbs
(not to be confused with ethernet data speeds which are different), and a
clock speed of 320Mhz. These cables do not contain an Ethernet
connection, but do include an Audio Return Channel.