Hate to be the first to post on this with a potentially stupid question, but I am trying to understand if I can plug my Iphone directly into one of the USB ports and then play Spotify, etc. The receive identifies and charges the phone but the message says "no USB"
I guess it is not supported and I will have to rely on Bluetooth?

The USB-A's are for thumb-drives. The USB-B is for computers. The USB-A's labeled ACCESSORY POWER is so you can power external devices like bluetooth receivers or other devices that operate on a 5V power supply.

You would not be able to plug a phone directly into the unit unless you have a headphone output.

When the phone app is released, if you have Spotify Premium, you will be able to directly send Spotify to the RR2160MkII via the app.

Next potentially stupid question. I am driving Magnepan .7s and they sound great although at the probably loud volumes I prefer, I have to move up to -20 to -12db with the volume knob. Will this be a problem for the amplifier long term?

Jeffy - I have found you can use the USB B input with an iphone and ipad to play music. One catch - You have to have Apple Lightning to USB3 Camera Adapter for it to work (needs a power source). Hope this helps.