I'm not familiar enough with these motors to comment on the oil consumption, but in general, 2 qts in 8k miles doesn't seem like an excessive amount. It really depends on the engine as some are prone to what many would consider excessive oil loss. There is also variability between motors, which is why some dyno higher or lower than others. My last car was a 2006 VW GTI with the 2.0l turbo motor and it used a quart every 3k miles. That isn't considered a problem however and from everything I've read, VW considers 1 qt every 1k miles or less to be a problem. I think the OPs best bet would be to head over to the mercedes forums and see how other vehicles using the same motor are performing. I personally have not lost any oil between changes, but the car has only had 2 oil changes.

This isn't the end of the world, IMO. You could always ask a mercedes-specific forum or a local mechanic who knows his way around mercedes cars. To me, the oil loss being described doesn't sound horrible. Then again, it's a fair amount more oil than I'm losing, which is imperceptible.