According to this wikipedia page, the Polish name Kac sounds more like "cots" or "kahts" than "cuts." As Kac is a Polish name, maybe @Borek can weigh in here.A bit difficult to write without pronunciation letters. In usual English "words" it is Kac = cuts.
What do you mean by "real e" and "real o"?Henneaux is a bit more difficult, as there is neither a real "e" nor a real "o" in English.
Not in terms of international phonetics:Isn't the 'e' in "be" a "real" e?
And isn't the 'o' in "go" a "real" o?
It's Russian: https://en.wikipedia.org/wiki/Victor_Kac [kats] and the "a" isn't spoken "open" as "cots" would suggest. But I doubt that Russian or Polish would make a difference. It remains an "a" (as in cuts), not an "o". The only point is, that he migrated to the US, so he eventually is spoken "cats" now.
It's still difficult to talk about pronunciation only by written words. "real" might have been a bit misleading, perhaps I should have said "proper". I referred to the way Latin is pronounced. There is no "e" in English, neither the French "é" nor "e" and at best there is a "è". And the same is true for "o". Consider "woman" ['u], "women" ['i], "no" [ou] and "Norfolk" [ˈnɔːfək]. All but a "proper" "o" as in "omen". And if you pronounce "omen" as an English word, there is still a bit of an "u" to be heard. Perhaps the German name "Otto" is the closest you can get.What do you mean by "real e" and "real o"?
Isn't the 'e' in "be" a "real" e?
And isn't the 'o' in "go" a "real" o?
Granted, both of these vowels have two pronunciations, with long e as in "be" and short e as in "bed" and long o as in bone vs. short o as in cot.