Dolby cannot be achieved with U100 or similar devices. Requires special hardware unfortunately.
Now, I would not say that Dolby increases sound quality, it is closer to sound equalizer if you know what I mean.
The stereo separation is exaggerated a bit so it is easier to hear, which is beneficial for video games.
I never got that far in BF3, but my brother played with some of the best players on youtube. He uses cheap earbuds and motherboard audio haha!
I would not worry about Dolby too much. You can always get a Dolby decoder like the Astro Mixamp, Turtle Beach DSS, etc.
EDIT: You should find more videos on youtube and make a decision. If you want Dolby, you might as well get the Essence, as you are not going to get a better soundcard
By the time you get the DG, DAC with optical input, and Amp, you are going to have an expensive mess. Go get that U100, don't look back!