After testing various archives and community forums, the and safest source for the Singer Futura XL580 software is Singer’s legacy FTP server or verified sewing machine repair sites like SingerOnline.com and EmbroideryHelp.org .
If your machine came with the "Autopunch" software (which converts images to embroidery) and you lost the disc, the free download from the Singer website will include it. It will only include the basic reader/writer software.