I have a Bifrost 2 Uber Multibit which has a AD5547CRUZ DAC (a true 16bit multibit). Both Schiit and other companies can produce DACs with an even higher number of effective bits, such as 19bit or beyond.
If the source is 16bit, would there be any advantage to having a DAC than has a lower noise floor or other properties (ignoring the quality of analog components)? Or would it be theoretically exactly the same?
The only possible theoretical benefit is that the DAC is less likely to introduce artefacts, as its resolution is considerably higher than the source.
I reality, this should be so negligible, I'd suggest it gives no difference to the listener.
No. And of course, "theoretically" it is not "exactly the same". But 16bit resolution is more than your reproduction and listening equipment is able to deal with.
Higher resolution DAC and ADC are useful in the audio creation chain. But if you are consuming a finished product, 16bit/48kHz contain more detail than you can discriminate and the weak link will be the speakers to a degree where the ability to hear quantization noise will not sensibly be part of any listening experience.
"Sigma-delta" converters (which the "Multibit" stuff likely boils down to) are dithering mechanisms. They offer excellent linearity at low frequencies but are quite more sketchy at high frequency components. But they are quite cheaper to produce than direct converters with comparable linearity so there is a whole buzzphrase industry grown around those reasonable compromises.
