little confused on the report filter, but I believe that what you are saying is that sum is summing all scores, not just the max for each employee. You can do this with shared variables, and probably running totals, but I am not real good with RTs, that is DBlank's forte.
For shared variables, you would build a formula that will 'replace' the aggregate for Max.
The formula would look like;
local numbervar thisTotal:=MAXIMUM({table.Score}, EmployeeGroup);
shared numbervar MaxTotal:=MaxTotal + thisTotal;
thisTotal
Where you want the sum of maxes, build another formula:
shared numbervar MaxTotal
HTH