When using the USB input of the A2+, what bit rate and bit depth should I set my system to?

The A2+ internal DAC handles up to 48K transfer rate, and up to 16 bits bit-depth. Your system will generally default to these settings when you hook up the A2+. If you mainly use 44.1K files, you might set this as the default in your system. Many system players like JRiver and Amarra will default to the proper bit rate automatically.