I believe this link will help with good insights on DTSx and Atmos.......
DTS:X is a next-generation surround-sound format designed to compete against Dolby Atmos. Here's everything you need to know.
www.cnet.com
In my opinion, I am sure the BR would have an option of other available audio formats to support / work on AVRs like DD or DD+ or DTS ...if not as per the article you have shared, the audio will come out like regular 5.1
I use a 7.1 SR series and only have 5.1 speakers set.....most content is DD or DTS and if your speakers are placed / angled properly, you would not be missing out on 7.1 or Atmos or DTSx effects....etc......as the 5.1 setup is already creating a decent envelope surround field...this is my opinion....others may have a different take!