From the new map wizard, when you make a dungeon map, you should now have templates for SS2 in there. When you create a map from one of those, you'll see that the catalog buttons load the new SS2 symbols instead of the DD3 ones.
You can also use these symbols in an existing non-SS2 map, to do this you'll have to load the symbol catalog manually by clicking the Open Symbol Catalog button, and browse to @symbols\Dungeons\SS2 folder to find the symbol catalogs.
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You can also use these symbols in an existing non-SS2 map, to do this you'll have to load the symbol catalog manually by clicking the Open Symbol Catalog