I think you looked at our qRules product at one point but didn't actually try it out, right?
qRules is going to help you out here but if I understand you correctly I think it might be better to sumbit the repeating rows from InfoPath into their own rows in SharePoint and then make sure you are setting an ID ("foreign key" basically) in those rows. This way you can do a mini relatinoal database using a flat list in SharePoint.
Make sense?
Ted