Before proceeding, it is vital to understand that Apple stopped maintaining standalone "version-specific" installers (like 6.1.6655) years ago.
You can download the zip file directly from the Apple CDN here: boot camp support software 6.1 6655 download windows 10
This downloads the correct version for your Mac, which may be newer or older than 6.1.6655. Before proceeding, it is vital to understand that
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