Try running minicom.

When the player starts up it will dump vast globs of data out the serial port. When it is running you will also see status info.

Make sure your settings are 115200, 8, N, 1 and NO FLOW CONTROL.

See this link for how to do it in windows.

When you can view the player status info, you shouldn't have any problems with the upgrade.

You didn't mention in your post, are you using the empeg supplied cable? If not, It must be a null modem cable.

Hope this helps
Peter