You need to let the tunnel 6 excavator breach tunnel 6. Essentially, you're letting the excavator open tunnel 6 to the outside so that the orb can "fall into" the tunnel. However, after the breach, the excavator blade will be blocking your access to the orb. Once the tunnel has been breached, you need to return to the receiving area (via tunnel 11) and hack the tunnel 6 excavator so that the excavator blade goes back up and out of the tunnel. At this point, you'll see the orb sitting in front of the door that leads to the power room (next to the M16).
From here you knife the orb back down tunnel 6 towards the receiving area until it's up on top of the receiving area on the tip of a sattelite. Then you shoot the orb off the sattelite with the wave gun so it falls down in front of the doors to tunnel 11. Then you shoot/knife the orb to move it down tunnel 11 into the pyramid room (FYI - Make sure to keep a close eye on the orb as you're moving it down tunnel 11. When you get the orb into the room with Stamin-Up the orb will dissappear into a hole in the ceiling. You'll need to pop it out with a frag grenade or by shooting it out. Just keep an eye on where it went into the ceiling and then shoot up around that area to get it moving again.)
Regarding the order of the steps - I always play the "Samantha Say's" game and hack the lab buttons immediately after turning on the power. However, if the tunnel 6 excavator breachs before you complete these steps - there's no worry. You just need to complete these steps before moving the orb down tunnel 11 and into the pyramid room (hacking the buttons in the labs causes the middle area of the circle-thing in the pyramid room to depress. This depression is where the orb will eventually land after you knife it down tunnel 11.)