I have a ASUS xonar u7 usb dac/amp. It has a very weak headphone amp capable of just 1.3 VRMS, so I am considering getting a separate amp like the JDS Labs Atom. On the line out, my u7 is only capable of 1 VRMS. When products are measured here, it is typically done at 2 VRMS. Would the SINAD of the Atom be different at input voltage of 1 VRMS rather than 2? I assume the output of the amp would only be half of what it would be, but does the noise level the amp adds depend on the input voltage?