It's not about making the music sound better anymore than getting rid of an internal combustion engine is about getting you there faster. Have you ever seen the size of the wires in a car that go the amplifiers? They're as thick as your thumb.

The move to 48V means much less power is lost (power loss = (IxI)xR ), cables can be much smaller, cables and terminals can be much lighter and much less copper can be used used.

Basically it's just a more efficient way of doing things.