Is there a way to take down an 80-X Boxguard and still get smooth/ghost at the end of the mission? I tried taking him down with an EMP grenade in several different ways (throwing the grenade below him, to his side, directly at him) but every time I would get "alerted" and "hostile" after throwing the grenade or after it detonated.
The best way of doing so, although rather cheesy, is to sneak past them and then finish the mission to get the smooth/ghost operator bonus. After that, feel free to go back and blow them up for experience.
I'm not sure if this is possible on all the missions as some may not allow back tracking (It's been a while since I played the game).