Wanted to thank you now although I have not tried any of this yet. Mother in Law lives upstairs where bonus room ( my computer lair ) is. She is in quarantine so maybe this weekend!
I did get some info from a guy on reddit which probably supports what you have told me. Dont know his specs ----
"Although not the exact same system, I started working on a WD Sentinel DS6100 this last weekend. Using loader 1.03b for DS3617 I'm able to boot and discover the device on the network, albeit with no drives detected. Reading around I find that I need an extra driver for the SAS controller which involves replacing the extra.lzma on the bootable USB device that I created. One hiccup for me was that Ioader 1.03b must be booted from BIOS/CSM mode and would not work in UEFI mode for me. I'm still unable to install the system, but in the 6+ hours of attempting this, those are a few things that I've learned along the way. "