Those 90% should riot in streets and demand standardization in amplifier gain. I didn't create that problem. Industry did. I am just trying to live with it. There are amplifiers with no gain above 15 dB. Are you asking that they don't get put in the chart regardless of their performance?
As to Purifi reference, there was no low gain in it. You could bypass the buffer but that is not the same as low gain and hence the reason it is not listed that way in the graph.
Also, since I have put amps with max gain of 15 dB in the chart, then it follows that I use low gain for other amps.
Finally, everyone better get onboard 4 volt output requirement since vast majority of proper DACs I test have that level of output. We need to move the industry in that direction, not fight against it.
Really, just live with an imperfect situation. Remember that the power of SINAD is not necessarily in the value itself but the predictive power it has to indicate excellence in engineering which is what we are after.