If the error message was: " '!' There are no USB devices available ", that means the unit was not in pre-boot. Some devices when bricked, including zumo 6xx, are tricky to put into pre-boot and need numerous attempts. The rule of thumb is that if you can see the logo splash screen you can almost always reach pre-boot mode too [eventually].

I'm a little suspicious that the other zumo 660 was also a BMW Nav 4 derivative and one of the 3 items in the changelog for v4.80>v4.90 is 'Added AVRCP capability to the Nav IV product'.

Thread marked solved.