"iSub now works again with 10.5.3!
This is just a followup to an earlier message. The iSub usb now works in 10.5.3. It shows in the system profiler as Harmon Kardon iSub, and works great on my iMac G4 1GHz. There are many of us who kept our iSubs hoping for a fix. I hope this information gets around so they do not get tossed!
-Scott"

BTW: Another iMac G4 owner later said to make sure the iSub was connected/powered -before- booting the system (rather than hot-plugging it). However like anything related to OS X updates, YMMV.
So far nobody with an Intel-CPU Mac has an iSub working w/10.5.3. (Also added a note to previous page on iSub Problems with Intel-based Macs (and workaround) in OS X Tiger.)

Update: After several owners of Intel-CPU Macs (including me) had no luck with the iSub, I asked Don to verify his friend's Mac Pro report of it working - he later replied it wasn't really producing sound. No KP as before, but no sound output either.

An iMac 1.8GHz (Intel) owner wrote his iSub (still) isn't working with OS X 10.5.3.

So I dug out an old iSub (original model from 2000) that came with a used iMac G4 I bought several years ago (never used it before). I tried it with a (2007) AL iMac running OS X 10.5.3 - it didn't work (no sound output) using a direct connect or via a powered USB Hub. It shows up in Apple System profiler under USB, but no sound output from the iSub (tested with iTunes playback, etc).

I then tried the old iSub with my (PPC) G5 tower running OS X 10.5.3 with a direct connect to one of the rear USB ports. Booted up, ran iTunes and the iSub did produce sound, but it wasn't good (intermittent, noisy/distorted, etc). This iSub may have a hardware problem, it almost sounded like a bad speaker connection. Nothing shown for it in the System Prefs->Sound controls either.