The number is actually -116 dB. Very few products actually get there. Best SINAD we have is 115 dB I think.If you claim that any signal or noise below -110dB is inaudible anyway, then what's the point in having better equipment?
That aside, the reason is simple: If you are going to spend $X on some audio gear, might as well get all the engineering excellence you can get. Once that goes beyond SINAD of 115 dB, you arrive a a point where we can prove, using psychoacoustics, that the system is transparent. Blow that number, you are dealing with shades of gray.
To the extent your solution lets us get to these superlative results, I am happy to recommend it. The key is to make sure that occurs in the analog output of the system, not some upstream measurement that doesn't correlate well with the DAC output.