If the user-accessible part of the chassis is metal then that has to be
bonded to mains earth.
2 core is only allowed for double insulated kit in the UK.
Its not a quality of sound issue but a health and safety issue first and
foremost.



I've never seen a piece of consumer A/V gear with a grounded power cord,
regardless of what the case is made of, but it certainly won't hurt anything
to ground it.


Maybe you ought to manufacture some of these obscenely expensive power cords
yourself, obviously suckers will buy them.