Davo, the Outcomes system allows for a simple identification of Met or Not Met (yes/no) for a student against an outcome. We've had overwhelming feedback that this simplification is needed instead of the current implementation that is tied to the gradebook and based on scales. In addition, the algorithm for calculation is left completely open ended - we'll develop our own implementation using a streaks algorithm, but that's just an example of one use case. I'm not sure how you're using a Unit - is that equivalent to a course section (i.e. topic)?
If I understand you correctly, I would use a Rubric that contains a criterion associated for each of the relevant unit marks. Each criterion would be associated with a P, M and D outcome. The instructor would mark off whether the student received a P, M or D, and the algorithm would mark off each outcome as Met or Unmet depending on the algorithm. It could do this even if the Outcome was used in different assignments or even courses (depending on how Units apply).
This might give you extra information in an Outcomes report as it would show each Pass, Merit and Distinction outcome as either Met or Unmet instead of showing each outcome as Pass, Merit or Distinction. However, you could probably customize the report in some way to get the information you need.