THX Spatial / Synapse doesn't output to sound card when Blackshark not connected

Ahoy. So I do have it set up correctly, I set THX Spatial as the default (though it does have two options,
*Speakers (THX Spatial)
and
*Speakers (THX Spatial Audio)

But this problem occurs on both. In Synapse, it asks me to select the output device to default to. I have an Asus Raid Strix 7.1 Deluxe sound card, and it has multiple output options - S/PDIF, Headphones and Speakers.
I have Synapse set to output to Headphones(STRIX RAID DLX).

However, when the Blackshark V2 Pro is turned off, it doesn't output to it. Audio plays in the system, and I can see it in the level-indicators, but there's no sound.
However, when I manually select the Strix headphone output as the output using the Windows 10 audio interface in the tray, the sound works just fine. Something is broken between the THX Spatial drivers and the audio output of the Strix. I've tried everything, changing the defaults, reinstalling drivers, to no avail. Would welcome any suggestions, or knowledge about this being a known thing.

Cheers.