Tori Amos, the singer in U.S., is described トーリ・エイモス in Japanese.
on the other hand, The Book Of Amos, Holly Bible, is described アモス書 in Japanese.
maybe, when listening in English, Amos is written エイモス by katakana, and when listening in other languages, e.g. German and so on, it's written アモス.
after all there are all sorts of each language's pronunciations.