Question about the headphone jack

Hi, can you watch videos via HDMI and listen to the audio through the headphone jack rather than the TV? This would be great for me so I wouldn't have to listen to the Power Ranger's theme song when my son is watching videos.

Also, I was wondering if I could use the Minix U1 like an advanced mp3 player. Is it possible to select a directory of mp3s for playback then turn off the tv/monitor and listen to them with a pair of headphones plugged into the headphone jack ?

Thank you.