There are a few links indicated in search results, here:
https://www.google.com/search?q=Griffin+iFire
While I too have those speakers, and three iMac G4 17-inch USB2.0
series late model 1.25GHz machines, the speakers are stored in box.
Original keyboard/mouse still find useful purpose as backup, even
though for various hardware reasons, none of my iMac G4s function.
{There had been a way to use similar speakers with the G4 Cube, or
so the story has been told. Not sure, but likely had a dedicated port.
As there had been pictures online years ago, showing these together.}
Thank you for bringing up the topic, as I have a Late 2012 Mini i7 that
has no speakers; so I leave it muted most of the time. Nothing to play.
And thanks for a refresher on the product from Griffin, in first reply.
PS: expect the Griffin iFire adapter to run very costly; you may find
a suitable PowerMac G4 Tower or maybe G4 Cube with the correct
plug/port for those speakers, for less money. Then use standard amp
with audio input, for a suitable source. For large hardware/less cost.
Best regards & good luck in this matter! 🙂