Ok, that’s a tad confusing, as they are called S1 and S2, not Sonos 1 and Sonos 2.
Your speakers can run only one or the other of these two operating systems, they can not run both simultaneously, which means only the controller that is the same as on your speakers will connect . You could have two different sets of speakers, one set running S1, which would connect to the S1 controller, the other set running S2 which would connect to the S2 controller.
There is a high possibility that Western Digital turned off SMB v1 in an update to your MyCloud’s software. If you’re not comfortable in looking at the control pages for your NAS, and making changes there, I would encourage you to connect with Western Digital’s customer service, and have them help you turn back on SMB and NTML v1.