Hey was wondering year and model of your car? If you are burning that much oil then you have a major prob. If you have a turbo I would check it 1st. PVC vavle can suck oil but that one pretty rare. More than likely you have some collapsed rings or very worn valve guides. You can take to someone who can do a leak down test on your cylinders to see how worn they are. I dont think a compression test would do because of all the oil going through(oil will cause psi to be higher because it seals up gaps)although if its one cylinder shot you may find it that way. You should pull spark plugs and note condition and which cylinders they come from. You should be able to find which one is burning the most by the plugs. Has it been fouling any plugs?
Good luck to you I think you may need it...........

One more thing to check, your air filter, a very stopped up one will cause it to suck air from any where it can and you will also have power lose..............

 

your problem might just be bad valve seals... you can actually change the seals without removing the head.. they sell a over the head valve spring compressor which makes the job a lot easier..... bad oil seals will let your oil enter your combustion changer and thats the cause of the dark smoke and burning oil..