So I am still a bit unclear as to the issue you're having. Did you test the BU-353 with the GPS Utility I mentioned in my last post?
If so, what happened? Were you able to select "usbserial" as the port?
And of course, you must have the BU-353 plugged in, in order for your computer to recognize it.
If you're still having issues, please provide some details as to your specific issue.