You may want to look at this thread:
Most of the parts selected will be quiet and pretty much fit the definition of what you are looking for.
As far as sound cards go there is none that have built-in amplification, or at least what I think your definition of, and instead pass-thru the signal to a dedicated amplifier that has support for things like Dolby Digital. Honestly, you would be better served to stick with the onboard sound card for now and see how it works for you and the home theater system you have. Too many make the mistake of buying more than what they need or do not have a good home theater system to backup their HTPC to start.