Hi Jurgen,
Unfortunately the qListView web part can only be filtered by one qSelector at a time, so when you try to set up a second provider-consumer relationship you will get an error message that the max. number of connections has been reached for the web part. I would advice to use the following approach to have qListView filtered by Level and ProductType.
Configure one qSelector as a provider to qListView and have it filter the list of products by Product Type. By Level I presume you mean the level of permission that user has over which products or what types of information about the products he can/cannot see. You could setup User Groups in Sharepoint for each of these levels, and use qListView's Show/Hider User Groups fields to filter what is shown and hidden based on the identity of the currently logged on user. You can also use this method towards filtering qListView to show or hide specific columns of the products displayed by qListView, which can be configured in the Display Fields property of ezEdit.
Hope this information helps, and if you have any other concerns please let us know.
Thanks,
Yuan