David Brin's Uplift War had a human fall in love with a bipedal tetrapodal alien. A curtain was drawn over their intimate encounter(s), but there were some comments about how just because people's reproductive organs weren't designed for each other, doesn't mean people can't work out some ways to experience stimulation. It helped that the non-human had some limited ability to manipulate her body, so she did things like shink her lower four breasts in favor of expanding her uppermost pair, because she knew he liked them best.
There was also an early-70s David Gerrold short story about a (human) guy in love with the idea of sex with alien women, and his search for someone with some compatible body parts (and, must be said, also compatible personality and desires). In the punch line he finds what he was looking for once he gives up one of his search constraints.
My impression from science fiction is that heterosexual men generally like the idea of more than two breasts but admit they'd find the reality confusing. Lesbians presumably cope better.
/there's a gendered multi-tasking joke in there somewhere
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/there's a gendered multi-tasking joke in there somewhere