Quick question for you,
A 9600GT with DVI to HDMI adapter
Did the adapter come with the card or did you buy it separately? If purchased separately and just a regular DVI-HDMI addapter that would be why you aren't getting any sound over HDMI.
Great guide on hooking and setting up here,
Guide: 8800GT/9800GT/9800GTX Sound over HDMI (Now including Creative cards) - Overclock.net - Overclocking.net