This crusty old beast was once a famed composer, but by the time Frobisher takes on an apprenticeship with him, he hasn't composed in over ten years. Ayrs is plagued with both "musical sterility" (10.5.5) and actual sterility, due to syphilis contracted over a decade ago.
Ayrs sees one thing when Frobisher ends up on his doorstep: dollar signs, or whatever sign Belgium used for its franc before the Euro. (By the way, see how important music is to Belgium? They had composers on their money.) Ayrs lets Frobisher do the grunt work while he gets all the fame and fortune: "You do the block-and-tackle work, I orchestrate, I arrange, I polish" (10.5.4). Yeesh, we didn't think capitalism and music ever shared the same living quarters, but it seems they do, and it's not pretty.
Frobisher thinks he's getting back at Ayrs by stealing his books and boinking his wife, but Ayrs knows about the affair and doesn't care. He probably wouldn't care about the books, either. Their loss is negligible compared to the renewed success he's experiencing from "Der Todtenvogel."
Despite treating Frobisher like a cockroach or a retail customer service associate, we think Ayrs might actually care a smidge for the little guy. Maybe it's just the teensiest spark in his ice-cold atrophied heart, but it's something.
The night Ayrs confesses his dream of the future to Frobisher (a dream that prophesizes the Sonmi-451 section), he asks Frobisher why he's even there. "You're young, […] you're rich, you've got a brain […] I'm not sure why you stay on here" (2.7.23). Frobisher then compares Ayrs to Verlaine and himself to Rimbaud. Verlaine and Rimbaud were a scandalous pair of poet-lovers with a tumultuous relationship during in the 19th century, so it seems as if Ayrs might mean that his feelings for Frobisher go beyond professional interest.
Here's the rub: this tumultuous relationship brings about some brilliant moments of creative genius. And that's what Frobisher needs. His creativity thrives under adversity, the kind of adversity that only crotchety old Vyvyan Ayrs can provide.