The software (Universal Scanner Audio Player) is for opening directories with sound files in them, and plays them. You need to plug in your trx or sds100 and copy the recorded files to a directory on your PC. Then use USAP to open that directory and play the files.
Or purchase
@ProScan for use with your SDS100 (and many other Uniden Scanners), set it up to record, then use Trunking Recorder to import from Proscan, and play back on your PC.