Digipan is FREEWARE so you get what you pay for. There are lots of other digi mode programs out there that are also free that will work well with the Signalink USB and also include many of the other digital modes.
The free version if HRD (Ham Radio Deluxe) is still available and I can personally attest to how well it does the digi modes... as well as rig control and logging.
http://www.hrdsoftwarellc.com/Just scroll down to where it says
To Download the free version, 5.24 Build 36, Click Here