If its just for music and movies it should be fine with just the 5.1 surround system connected to the optical output of your laptop. I'd make sure that your 5.1 Surround system supports optical input.
You only need the external card for 5.1 gaming.
The build in sound manager will be fine for setting it up
The HDMI does output 5.1 sound so if the 5.1 Sound System has HDMI input you can use that but in most cases it will use an optical input which the headphone jack on the laptop also doubles up as, you would need an optical 3.5mm to optical on the system