If you had a higher end receiver, it would be amplified. But honestly, multiple zones on most receivers are difficult to manage.
I don't think its for echo cancellation, I think its just for monitoring.
The Pi isn't a good option at all. (I have one and use it for this purpose!)
Remember, you still need to provide a USB power source (2A or above ideal), USB WiFi, case, and you might also want a remote (yes, you could use your phone as well). After you add up the parts, you might as well get...
Does he have a laptop? Does he have gaming machine?
If he has a laptop then the solution is easy - just setup a share and have him using an HDMI cable.
If he has a gaming machine - 360, PS3, etc then he can use PS3 Media Server or whatever the name is now.