"I would not lay the blame on USB sound or the SoundSticks themselves. My set had problems with the sound cutting out intermittently, and Harman Kardon told me that the SoundSticks should not be connected to a hub. They need a dedicated bus. Given that USB only has 12Mbps, this made a lot of sense. I moved the speakers to one of the ports on the Mac (since each port has a dedicated controller) and the problems with the speakers went away.
It seems that USB sound is not the only thing that needs dedicated USB controllers. I was having all sorts of problems with my new 677MHz G4. I had a PCI card and 2 hubs connected to my G4. I replaced the card because it only had one UCB controller for two ports - the card was basically a hub. Note: You can see this in the Apple System Profiler.
I now have a TurboQuad USB card (well worth the $40) with four ports and USB controllers - (one per port). This gives me a total of 6 ports with 6 USB controllers. My experience is that any device that needs continuous communication and does not recover successfully after another device hogs bandwidth requires a dedicated controller. This setup has allowed me to attach nearly a dozen USB peripherals to my Mac without a hitch."
Update: Max Killen received the following advice from Harman-Multimedia on troubleshooting problems with SoundSticks:
"Make sure you have virtual memory turned off. Also, do not plug the SoundSticks into a USB hub. Plug them directly into the computer. If the SoundSticks are plugged in, it will disable the headphone jack. If you haven't done so, try upgrading to Mac OS 9.1. It looks like something is conflicting with the SoundSticks (possibly software) since it is also conflicting with your headphone jack."
Mike Robertson adds:
"Apple Tech Support had me swap the video card (a Rage Pro) from my G4 450 with the GeForce3 card in the 733. Using the older card in the 733, the DVD played fine using the SoundSticks. No pops or wavering of pitch. I put the GeForce3 card back in and the problem returned. When I asked if there were any new drivers for the GeForce3 card, I discovered there aren't any new or old ones. The drivers that shipped in my unit are GeForce2 drivers. New GeForce3 drivers are due out 'soon.'"