I am using GPO in Sonar PE4. I have trouble remembering how I loaded instruments and only see the first few letters of the instruments names in the player. I looked at the file which is named for the instrument group (my named) and all there is in there is a lot of characters, but no words in any language to define the instrument names.
I'm not absolutely certain I understand your problem but each slot of the player displays 16 characters. Some names are longer than that but if you click on the instrument slots in the player the full name will display in the larger main window in the player. For instance, Marimba Grand Symph KS will display in any of the 8 slots as "Marimba Grand Sy" but the full name will display in the main window.
Here's a suggestion for Sonar: Always label your MIDI tracks with the GPO instrument name. That way you will know which instrument you intended to use on that track even if something goes wrong with the GPO VSTi and you lose the loaded instruments. Or if your memory comes up short. Sonar's track label window can be resized to accommodate even very long names.