Cant get 5.1 audio configuration over HDMI for Windows 7 (64bit)

I am using Win 7 Home Basic - SP1 (64bit) Vaio laptop with ATI Radeon HD 5145 graphics/audio card. When I plug it in to my home theatre through HDMI there is only a 2.0 sound configuration, there is no option for 5.1 or Surround sound configuration.

My home theatre is a Samsung HT-X70 (its capable of dts-hd 5.1 and Dolby Digital). How can I configure the HDMI to 5.1? Appreciate any help, I have spent full week to make it work but am all lost.

More Details:
1. I have already made HDMI Digital output as default playback setting (see attached snapshots)
2. Tried reinstalling drivers for HDMI sound, but still the option wont come
3. Tried installing Realtek Media Center from CNet (link) but this wont install on my laptop giving "No driver was support in this package" error.
4. And no, I dont have that Realtek Media center UI which people recommend to use for changing this configuration. I have tried installinbg Realtek's hidef codecs realse 2.65 and 2.67. 2.65 wont install giving "No driver was support in this package" error (as mentioned in #3). 2.67 installs but nothing changes on the system and no media center is installed either

I have the same problem with my sony home theatre.

Jassi, have you looked at this thread? It may give you some ideas.

It's a different video card but the solution may be in older drivers.
http://www.sevenforums.com/sound-audio/65714-hdmi-not-plugged-my-solution.html