what Xan asked for was the original OLTP source in SAP R/3 or ERP, not in BW. This is an extractor that is BEFORE the data is in the ODS object.
Unfortunately I can't help you with your problem, but when I want to extract several millions rows from an ODS object, I would use the "Open Hub Services". the OHS are designed by SAP to handle millions of rows for using in external Data Marts (e.g. QlikView). As far as I know, there's no limitiation regarding the size.