Did you make the one line "tts" script as described? If you did test out your "tts" script by issuing a: tts "hello world"
on the command line to make sure it's working (i.e. you should hear it play). Also make sure you edited the roadmap preferences file and added the appropraite lines.
If all else fails you might try watching the console when GPS data is coming through- to do this you will need to run RoadmapGPSApp in a telnet session and maybe use a GPS simulator like NMEATool. This way you will see the Error messages that Roadmap returns when it can't run the configured tts binary.

BTW- the Roadmap trip error is normal, it happens because the Empeg doesn't have a writable hard drive.