When using Magmi the value in the column attribute_set is always imported with the value default while the values in the import file are defined as attribute_set in the backend.
Example:
The attribute_set value banden is always imported with the value default.
Example of the import file:
store attribute_set category_ids sku admin Banden 3 BF2156516HLON
I tried with _attribute_set as wel as with attribute_set (with and without underscore).