I have pretty much decided to buy a pair of Beyerdynamic DT990 pro headphones. The question is, which version? Most people seem to favour the 250ohm model. Is there any difference in sound quality between the 250ohm and 80ohm models? I don't have a headphone amp at present but would be willing to buy something inexpensive such as the Schiit Magni if the 250ohm model sounded better. Any views or comments most welcome. Thanks.