I had our lead design engineer take a listen. He said that it sounds pretty normal, considering the 40dB boost to get that hiss on analog.
The reason you don't hear the noise floor on the digital I/O is that we just send zero's when the gate is closed.
If you turn the gate off, you'll hear the actual noise floor of the signal on the digital path.
The only advice they gave is that you should always have your output level maxed to give you the best SNR, coupled with as hot an input signal as you can get before clip.