Help getting started? AUDIO ISSUE

Imac Pro
High Sierra 10.13.3
Desktop Video Setup 10.9.11
Blackmagic UltraStudio 4K
Final Cut Pro 10.4 is preferred edit program

My problem is with audio.

My system is pretty simple. No decks. Thunderbolt connection b/t iMac and Blackmagic. Mackie mixer. JVC studio video monitor connected to Blackmagic through SDI. Audio monitors out of mixer.

Playback works fine. From iMac thunderbolt to blackmagic to mackie mixer to speakers

I can't get an audio signal recognized at the iMac from Blackmagic. Not in FCPX. Not in System Prefs (Sound.)

The signal IS getting to the Blackmagic (if I unplug one of the inputs and plug that xlr into my speaker, it plays the signal)

I've consulted the manual, but it is not helpful. Seems inaccurate from the start. I'm using a thunderbolt input and there is no thunderbolt icon in the Desktop Video Setup box. Makes me think they've taken some shortcuts. I've also read I should capture with something called Blackmagic Media Express. Can't find it on the download page and I don't want to use an additional program anyway... that is probably old info. Any help would be appreciated. I've been working around this problem for days.

Not sure if this is helpful, but Blackmagic Media Express is automatically installed with the Blackmagic Desktop Video driver. Check your applications folder. Also, you need to pick the signal the Blackmagic Ultrastudio 4K is getting for audio (embedded, xlr etc). Thunderbolt is just the connection from Ultrastudio to iMac.