In Windows Sound, Properties of your monitor > Supported Formats. How many channels is it reporting as Max?
Check that you have configured the number of channels in Windows Sound. Cant remember what is default (2).
Enable Surround Sound on the TV without your external Amp, and you should hear all 5 channels from the TV even if it only has 2.
It's reporting 2 channels as the only options on windows sound. Surround is not an option. I also checked on my flat screen sound option and it did not give surround as an option either. When I go into sound under control panel and right click on amd hdmi output which is to configure speakers it only has the option for stereo were as before it had an option for digital surround....