My unit has been on 24/7 since I got it in March. I'm very satisfied with it. Initially it was on max gain, but I've lowered it to have a reasonable max volume on the receiver.
Not sure, according to the manual these are the values :
PRE OUT (Output level/output impedence): 1V / 1.2k Ohm
https://europe.yamaha.com/files/download/other_assets/0/329200/RX-A830_om_UCRABGLF_En.pdf
I run it with max gain, that was how it was configured when I unboxed it. No white noice at all. I've connected it to the pre-outs of my receiver RX-A830 with unbalanced pre-outs. I'm very happy with the A2-400.
XTZ said that the first batch was small. A bigger one will arrive in April (if its not stuck on Evergreen). As long as they sell out what they can produce I guess there is no need to send one to Amir.
I had the A2-300 earlier which I sold. I felt it was on par with my receiver, a Yamaha RX-A830. The A2-300 required a lot of gain which led to hearable white noise. The A2-400 is a different story, no problem at all to drive my Arendal 1723s towers. I'm able to play louder than I ever would want...