These programs need unfiltered raw audio and a speaker output has too much passband filtering and de-emphasis to allow the digital waveforms to pass without distortion. So that's why you need a discriminator tapped scanner. 15 years ago this would have been the way to decode DMR before it finally came to scanners.
If you have a ham rig with a 9600 baud output, that will work in lieu of a scanner with a tap. But as everyone else has said, there isn't much reason to go through this pain anymore when you could be online and decoding with an SDR stick in a few clicks.
