In this case, you would need to check if your computer recognizes the Technaxx TX-20 card as a sound input, then on the program you would need to select that device as the input device.
If the program does not see the Technaxx TX-20 card as an audio device, it is likely that the drivers from that device are not compatible with Debut.
At the moment, the program does not have an option to force the driver, so you may want to check with the Technaxx TX-20 card manufacturer for a driver update.