The first place I would check is the sound card settings. Go to setup --> soundcard --> sound card devive (yes, it appears that they misspelled "device"), select something other than what is currently set up, and then close and restart the app as instructed.
My issue with running DIGTRX on Windows 10 is that the decoding process seems to get stuck on a loop and it never finishes. I have better luck on my older Windows 7 machine, running the older version of DIGTRX that's compatible with that operating system. I may have some basic setup problem that I have yet to figure out on the Win10 one, or perhaps it's a problem with the last version of the program. Who knows? I think it's been 11 years since the author of that app abandoned it.