10.5 bits is 1 part in 1448 or 0.07% so in terms of something like THD you could argue it is below our threshold detection for a full-scale signal. But it also means noise or whatever is only 63 dB down so may be audible at lower levels depending upon the cause of the distortion and how it tracks with amplitude. The point I (and many others) have made before is that either way, given the number of inexpensive DACs that measure much (MUCH!) better, why pay for one that does not?
I suspect "Amir bits" is in reference to Amir's linearity deviation plots which are not based on ENOB per-se (he does not measure ENOB directly IIRC and the metric for deviation is not 6 dB but something lower). I have known and used ENOB for ages but it is not the end-all be-all spec and as long as I know what Amir is doing his scheme provides a good relative reference for comparisons among products. Which is all most of us want anyway.
IMO! - Don (well, the math is not opinion, but check it...)