Atmos setup in Windows 10 won't access all my 7.1.4 channels

I run an Atmos 7.1.4 monitoring system in my composing/mixing room using Steinberg Nuendo, which works fine. When trying to setup Resolve 17 Studio's audio, the dropdown for Speaker Setup only shows my Windows 10 audio stereo configurations. So even though I can choose my RME Fireface UFX+ which has a LOT of outputs, it only shows a couple of stereo choices and I can't fully configure 7.1.4. Am I missing something? Is there a way to get Resolve to see my entire audio interface? I've seen it in a video working correctly, but I think it was a Mac, not PC.

Hi Paul, I run 7.1 with Solid State Logic converters, but Resolve doesn't support ASIO, so I have to use the SSL's WDM drivers for windows. If you right click on the speaker icon in the task bar and go to sound settings, see what output devices you have available. There should be multichannel WDM drivers for the RME (provided you chose to install them when you first ran the drivers installer), but I'm pretty sure WDM can't support more than 8..I've only ever seen it up to 8 channel. Under ASIO with Pro Tools I can access all 48 ins and outs on my converters, but not with WDM drivers. Nuendo will be using the ASIO drivers, so different story there.
I believe you may need to use the Fairlight Audio Accelerator card plus a set of MADI converters to access more than 8 outputs, but don't quote me on that..there are a few other audio guys on here so hopefully one of them knows a little more about taking things beyond 8 channels. At the studio I work at they have the accel card and Fairlight converters and get over 8 outputs.