If the hiss is constant regardless of gain, then hiss will be very noticeable at lower volume settings because there is little signal to mask it. If you have very efficient speakers, you will use the 950 at a lower gain (volume) setting. With the lower setting, the hiss is greater in proportion to the actual signal, but the amplifier sends both the noisy hiss and the lower signal to the speakers, causing the hiss to be very audible along with the signal.

Conversely, if the hiss level changes with gain level, it will be less at lower gain settings, keeping the hiss quieter when listening at low levels or with very efficient speakers.

Add to this the lower noise floor AND the greater gain that Soundhound measured, and you come up with a much quieter unit. (one that is about 40% as hissy as the old units at normal listening, but should be extremely quiet at lower listening levels!)