The general rule of thumb is: white smoke = water, black smoke = fuel, blue smoke = oil.
Admittedly I think sometimes if you have clouds of oil smoke, it looks white, but in that case the smell will give it away.
So, it could be headgasket (or possibly a cracked head) if the "smoke" is water vapour. The lost oil could be caused by the same problem, although it does sound rather a lot.
If the smoke really is burning oil, then the likely problems are as you say are the turbo, or a piston. Piston failures are rare on 9000's it seems, to the turbo has to be the first suspect.
See if you can tell if it's water vapour or oil smoke coming out.
Have a look in the air intake pipe leading to the throttle.. is it full of oil? Also try taking off the pipe from the air filter at the turbo and look inside. Is there a lot of oil in there? Can you turn the blades freely?
I'd also suggest trying a compression test dry, and then repeating with a drop of oil in each bore to see if it makes any difference.
Hope that helps.. it's somewhere to start at least.