Uniti 2 input level

Hello all. New here so any advice much appreciated.

While setting up ipad via airport express to Uniti 2, I noted that the input level on the Uniti was set at a rigid 72. A moment later I hit the mute button as airport express suddenly configured, almost streaming my new speakers into darkness. So I minimized the ipad output level to compensate, halved the Max output volume on the Uniti.. Streaming / iTunes is all sounding pretty good but I wonder, 

• Is 72 a level preset that cannot be changed?
• Perhaps to optimize gain structure / control Signal to Noise Ratio??
• Is there another way of dropping this level or compensating for it within the Uniti?
• N-stream sets this input at max too. What am I missing here?

I am concerned going forward that an oversight by myself or sig other may blow a speaker cone or two.

• Any ideas? 

Cheers in advance,

Davy