There is no ground on the amplifier. This is called a ground lift, and is fine. They still use a standard D-type plug, like you find on all PCs and a ton of other gear, because power cables are cheap and readily available.
This is typical and common on many products, and my Denon receiver and I believe my Rotel amps are similarly designed.
If you look at the pictures of the back of the amp on their website you will see picture 4 is of the back of the amp and it only has the two pins. That's the hot and common, no ground. Just as it is supposed to be.
http://emotiva.com/xpa3.shtm
You are fine!