Exactly my issue! This is why I'm at least looking for the USB Audio Extension, which should be integral in most iMac and PowerMac G3 installs, at the very least-- Unless the features from this are integrated into another USB extension I don't know about. I know for a fact I was able to get my G4 Cube to use the iSub waaaaaaaaaay back in Classic 9.2.2, but the hard drive to that thing is long lost in my plethora of stuff-- and the only known backup of it is long since gone. I'm not sure if I ever made a copy of any of it to my Mac Mini, let alone my G4 Cube, so that's another issue I face right there.
I also have a couple of iMacs (iBoatAnchor G3 350 non-DV) in the attic and at least one 500MHz snow, I'd have to look and see if any of them have any sort of working 9.x install. I know at least one that's in my care in the BASEMENT at the least has a drive I know to have 9.2.2 on, but I'd have to get RAM for it and dig it out of all the clutter. it's just too much work, especially if I can get it from somewhere on the internet from someone that owns a G3-era oldworld/newworld Mac with a running 9.x install AND that extension-- it'd be the ultimate silver platter option, especially since I have 0 idea if these have that file of which I seek.