Bamboozlement in progress.
I do not dispute that because I dunno shit about any specifics. I have never seen an ADC or DAC that was not inherently fixed point. All’s I’m saying is that I can conceive of a couple of ways it might be done and not be simply a gimmick. For it to not be a gimmick, it means that, to within 6 dB, the signal-to-quantization-noise ratio needs to remain roughly constant over a wide range of input amplitudes. I.e., dB S/N should not be a quantity traded with dB headroom, for a true floating-point ADC or DAC.
If the S/N increases as you trade away headroom, it’s essentially what a fixed-point ADC/DAC will give you, whatever format the numbers going in or out have.