Yeah 6.3V should be fine as 5v is all it should ever get. My 6,3v cap hasnt blown up yet Use your own discretion.. 16V would be the safe choice.
As for the static bags, yes they make a difference (the thick semi-transparant silvery kind). I'm not sure putting a 'static bag *over* the card' is such a great idea if that is what it sounds like. It will get too warm and cause some distortion (tried this). Probably only covering the backside of the card is plenty, maybe could do the DSP/DAC also but i dunno if its needed. But dont smother the card.
Edit: Anti-static bag now installed.