if you do see oil on your frame or anything, buy an oil dye kit and use a black light to find the leak, makes it a whole lot easier, specially if you have a garage you can fit the car in to block out some of the light.....

if its burning it, you should be able to smell some oil with that high of consumption.... but run a compression check, if you get low numbers then you should run a leakage check on each cylinder with a low number to isolate weater you've got bad rings or not..... once thats eliminated... go ahead and pull the intake manifold..... trying to give this in an order that will keep you from pulling things apart without need