Let's pick 2 amps - one has a SINAD of x, the other is only 0.7 x but it is played 0.5 dB louder
which will be preferred?
or use THD levels, etc.
SINAD will not tell you which electronic equipment you will prefer. For that you have to listen. You may even prefer one with 0.5 x...
Besides the amplifier performance will be impacted by the load so it must be listened with your speakers (in your room) or your headphones.
There are no free lunches in audio and no star-rating, SINAD or Speaker Preference Rating will provide the magical answer that you are looking for.