Hello Jacco,
What is the error from Solution Manager when you try to generate the XML file? If the error is not visible switch to Log tab and see what is the cause.
Have you extracted the files to EPS/in using SAPCAR? Also you might need the attribute change packages, but as far as I know this add-on is asking for a XML file during installation with SPAM/SAINT.
Try to add PLM Core as Product Instance under EHP7 FOR EPR 6.0 (add-on) in your Solution Manager configuration for the SAP System in scope. This should be possible by executing transaction LMDB in Solution Manager System and selecting your ABAP System. After this execute a verification check and proceed with the mopz calculation if everything is green, in case the status of verification is red try to fix all the issues until the status of verification check covers all your software components.
Another possible way would be to execute the verification from LMDB for your ABAP System and see if the current configuration from Solution Manager covers all your software components, if yes, go on with the calculation of XML file and select/assign PLM Core to your System when you will reach Add-on Selection step.
Best regards,
Marius