I just tried it, but the maps from eniro.com won't work. Even if I could figure out the coordinate system, the server does not let you request maps of an arbitrary size.
But I don't know why you're disappointed in the maps that are already available. Here's what I got for Katrineholm's coordinates:
(If your map covers a wider area, you won't get as much detail. But on smaller scales, you're not going to find anything better than that!)