Yes I get what you mean..I'm using a 750gb on the Zgemma and works great...
A little tip incase you come across members stating they can not record one and watch another ppv channels..I recon it's because they are putting LNB feed into wrong input connecter on the back of box..they are putting it in the loop out connection as its inline with the other tuner..
But as you know it needs to be in the top input..