Here's where you might annoy the sales reps, but when's the last time they paid attention to you? While you're watching that video, crank the volume on the notebook, and see if it sounds like an IMAX theater or a transistor radio. Second, where are the speakers located? If they're on the bottom of the notebook, chances are they'll be muffled when the system is on your lap.
Try playing a track or two that's preloaded on the system under the Music menu. Briefly, crank the volume to the max or close to the max to see if the sound is still clear or distorted. Also, check the Start Menu as well as the Control Panel to see if there are any utilities such as Dolby Digital or Beats Audio that let you tweak the sound. If so, fiddle with the settings to see if you can get it to sound just how you like.