When Apple released some of the final updates to OS X 10.5 for PowerPC systems, a number of Harman Kardon iSub owners found their speaker systems no longer worked properly with their computers. The problem appeared to be a driver-related error but neither Harman Kardon nor Apple stepped up to fix the issue and owners had to resort to other speaker systems.
iMac Core Duo (Early 2006) Special Report: Problems with iSub -- potential cause and fix
iMac Core Duo (Early 2006) (#3): Safe sleep available; Problems with iSub
Troubleshooting GarageBand: iSub distortion
Digital Audio Problems: Recording Play-Through; Muting the iSub
Digital Audio Problems: More on Muting the iSub; ViaVoice a Culprit?
Mac OS 9.2.1 issues: DA fix; iSub performance; more on SDAP extension; DVD player stops working
New & Noteworthy: REALbasic; iSub price cut; PlayerPro; Opera reviews
Odds & Ends: Retrospect issues; CarbonLib; iSub; Quicken 2002 securities list bug?
Stand-alone iSub will not work with G4 Cube speakers