Has anyone heard of the "Apple AV system"? Is that the card in the AV Macs that gives them those abilities? Which Macs does it work with?
When I bought my PPC 8600 some time ago, it was advertised as an 8600/AV. Basically it had "personality card" in it that had (and I don't have it right in front of me right now, but...) audio in and out as well as S-video in and out. The beige g3s had them as an option as well. There are also various other PPCs, Quadra and Centris models with the AV tag, though I don't think they all had the same options.
Basically it had “personality card