How to Bypass the Bug Affecting Garageband on PowerMac G5 Quad

Hereafter is a report from Clément:

Garageband (08 or 09) was not working properly in on PowerMac G5 Quad after Mac OS X 10.5.6: very slow almost frozen system, audio/midi preferences not available, only 2 seconds of recording or playback. Making a clean install of Leopard and Garageband does not help, neither repairing rights on HDs, files or folders, deleting prefs files etc. All PM G5 owners were complaining as illustrated in this post: http://discussions.apple.com/thread.jspa?threadID=1788989&start=0&tstart=0

Till this message: http://discussions.apple.com/thread.jspa?messageID=9734914?

Amazingly, one just needs to connect the input and output with an optical fiber to solve the problem. So a bug in Leopard prevents the proper use of audio digital ports on PM G5 Quad. This bug affects Garageband, but Soundtrack Pro (part of Final Cut).

Let's hope that future update of Leopard will fix the issue, as it will be the last OS X version to support PPC-based Macs.