Hi/low sensitivity and ground toggle switches???

I was just wondering what it was for. I have a toggle switch on the back of the preamp that says hi or low. Which one should i be using. It sounds a bit louder with it on high. Also there is a ground toggle switch on the back. What would that be used for. THis is a audio innovations l2 tube preamp. I have a sonance 260 ss amp. thanx for any info. Kevin