Karoline -
What you might be thinking of is for a shareholder-employee in an S-corporation, they receive income both from their services as an employee (W-2) and from their investment as a shareholder (K-1). For that scenario you would only use their W-2 compensation.
For partnerships, including LLPs, compensation is defined as net earned income, which is calculated in the usual way: K-1 earnings less one half of self-employment taxes, yadda yadda. Be certain to account for the portion of FICA taxes that were paid on their W-2 in order to accurately calculate the self employment taxes.