wow, I'm glad this thread is continuing! It took a few days but I finally got my replacement serial cable. And my "cat /dev/ttyS0" stuff did work. All it did was print out some garbage which was enough to tell me that it's active.

I couldn't get it to work via virtualbox so I grabbed the upgclient and yeah, that doesn't work either:

Code:
$ ./upgclient  Windows_Share/builder_bigdisk_v4.upgrade 
empeg-car Upgrade client.
empegupgrade: Using upgrade file 'Windows_Share/builder_bigdisk_v4.upgrade' to device '/dev/ttyS0' (115200 baud)
 Checking upgrade file integrity                                        [100%]
Pumping player software
 Finding unit                                                           [  2%]
Upgrading flash (bootloader)
 Erasing flash                                                          [  0%]
 ERROR: 8 Flash erase failed                                           
 Upgrade aborted due to errors                                          [  0%]
Upgrade failed :-(

Upgrade failed with error 0x80040057


Any ideas?