"Simple" discriminator output being the operative word. GRE shouldn't be calling it "discriminator" output, really. What the PSR-600 (and others like it, thru the PC/IF USB port) output is trunking command data in ASCII (text) format. In an application like DSD, you need the actual raw audio sound for DSD to translate.
If you are looking to buy a scanner that is ready to go with DSD out of the box, the PSR-800 does output raw audio (true "discriminator audio") from the headphone jack when properly configured.