As I'm writing this I'm also playing my stereo that has a phono section, a line preamp and dual mono power amps that all have switches to lift the chassis grounds. Those mono amps always play with the ground lifting switches in the lift position, because they sound better that way, in my system that has extremely sensitive speakers.
As far as I am aware what those switches do in all of the audio components which provide them is to isolate their internal circuit ground from the chassis, while not affecting the connection of chassis to AC safety ground. And consequently setting those switches to the lift position does not defeat the intended purpose of the AC safety ground, which is to cause the breaker to trip if an internal short develops between the AC line voltage and the chassis.
Regards,
-- Al