I use an Tascam US-16x08 USB audio interface on my Windows 10 Computer and with programs like Ableton it works fine. But a lot of other programs like 'slack', 'discord', ZOOM, Webex, etc. have a problem to use these inputs. The best would be to have a virtual mixdown from the multichannle audiointerface to a singel virtual stereo audio input for the PC. Has someone an idea how or with whicheprogram I do this? I was not successfull during my web search.
It is probably possible to do in the mixer in the Tascam. Check the manual.
If nothing seems to work I would do like this. Mix inside the Tascam and output to two out channels. Connect with patch cable to input 1 and 2 (or whatever channels shows up in the other programs). You loss two input and 2 output channels that way, but better than nothing.