Fortunately, Sonnet maintains most of its software for download. You need the extension Sonnet Processor Upgrade v3.1 in your Extensions Folder, with a space character in front of its name to make sure that it loads immediately after EM Extension. Because the Sonnet installer may not remove an older Sonnet extension, you may have to remove one such manually, if it is present.

I have three L2 G3/400MHz 5500s running quite happily with this software.

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