There are two ways to pronounce this name in The Netherlands, which depends on where in the country you are located.The first possibility is: AHM-bro:sThe second possibility is: ahm-BRO:S.
Well, I was able to dig up some YouTube videos where the name is said at least once. There was very little material available, but so far it seems that the stress is usually placed on the second syllable:/ɑm.'bro:s/This is clearly in line with the Dutch pronunciation of the source name, Ambrosius:/ɑm.'bro:.si.ɵs/However, despite this, there are still some people that place the stress on the first syllable of Ambroos. I guess this means that in the end, it really depends on the bearer where the stress is placed, i.e. there is no fixed pronunciation for Ambroos (at least not like there is for Ambrosius).Here are the videos in question, so you can hear everything for yourself:• https://youtu.be/nvlSPPNU8QU (in Dutch; the man is Flemish and the name is said at 0:10 → the stress is on the first syllable)• https://youtu.be/Jv9bTR1jRdE (in Dutch; the man is Flemish and the name is said at 0:18 and 1:43 → the stress is on the first syllable)• https://youtu.be/YlRdQnhancE (in Dutch; the female narrator is Flemish and the name is said at 0:35 and 1:06 and 2:01 and 2:30 and 3:09 → the stress is mostly on the second syllable, but sometimes on the first)For the sake of comparison, here is audio material for Ambrosius:• https://nl.wiktionary.org/wiki/Ambrosius (in Dutch) • https://nl.forvo.com/search/Ambrosius/nl/ (in Dutch) • https://youtu.be/5Cp35TG5wT0 (in Dutch; the woman is Dutch and the name is said at 0:02) • https://youtu.be/ED_g1dz3aMo (in Dutch; the male narrator is Dutch and the name is said at 0:38 and 1:33)
The first possibility is: AHM-bro:s
The second possibility is: ahm-BRO:S.