Data Exchange framework - File with more lines

Hello ,it's me again about Data exchange framework...When I want to export payment file from payment journal,to make .txt file with Header and Detail Line,NAV demands from me to choose only one line definition,even thou i have defined two.(This is set up in Payment Method)So when I export I have only data from header or from Detail line...Is there any way to link these two lines in Data exchange definition,or this setup in Payment Method needs to be improved?