Yes, XS++ doesn't have w580i custom pack but can use your own custom pack.
Download your custom pack ..your favorite....
Create a folder called "own_custpack" in XS++ dir.
Unrar the contents of the custpack you downloaded early to the directory just created. So you will have \own_custpack\tpa\preset\custom\
In XS++ select "own_custpack" from the drop down box. Flash!