HD video is purely based on your GPU, and most onboard graphics are more than good enough for 1080p these days (with the exception of some of the older Intel graphics bundled with Atom CPUs).
For audio there are 2 routes to take;
1) get a sound card that has hardware decoding for these formats (Creative, tutlebeach, etc). This has the advantage of generally being faster, less CPU intensive, and tends to come with some great software that will clean/boost your audio.
2) get a mobo with digital audio output (optical or spdif... really they are both spdif and one is optical and the other is coax, or run audio through your HDMI output). The audio will be rendered on the CPU, but even on a crappy Atom it would only take ~5% CPU usage, and as it is all digital there should be no issues with noise. If you want software to clean up or change the audio to sound less dry than a pure digital signal then Creative sells something called x-fi MB2 ($25, the order process is wonkey, but you will get it) which basically takes all the goodness of a Sound Blaster or Audigy card without having to deal with all the driver issues, and other quarks that Creative is known for.
The board you picked is no longer in production and seems to go for $120-180 from what I see online, which is far too high unless you absolutely need the features on this board (like eSATA).
I would suggest something like this: $85
http://www.newegg.com/Product/Product.aspx?Item=N82E16813138335
It does not have eSATA, but does have everything else you could need. It also comes with a remote, and an IR sensor if your case does not already have one (and if you case does have one then you can plug it directly into the mobo)
Then pair it with: $85
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116398
More than enough CPU power for movies, internet, and flash games. Otherwise you could stick with the one you picked for a better GPU to open up light gaming.
Best of luck!