1. Processing virtually always occurs at 32bit or 64bit, regardless of whether the source files are 16bit or 24bit. So, the artefacts are at exactly the same level regardless of a 16bit or 24bit source!
2. Sure, but of course that's the freq response of your HPs (or speakers + room), the freq response of your ears and your personal preferences, which has nothing to do with the source file's bit depth!
3. Firstly, there is no mechanism/process which could cause that effect and Secondly, it is easily verified (with a null test for example) that the "sound to your ears" is identical with 16bit or 24bit. The only difference is ultrasonic content (above about 22kHz) and very low level dither noise, BOTH of which are inaudible (to your or anyone else's ears) at reasonable listening levels! The only rational explanation is therefore that you are "hearing" some difference that occurs AFTER the "sound to your ears", EG. Some bias in your perception.
3a. There are two conditions under which it can be possible to ABX a difference between 24/192 and 16/44:
A. Using a 24/192 recording with significant frequency content at 22kHz or higher that is causing IMD in your amp or speakers (within the audible spectrum) and comparing it with a 16/44 conversion, that obviously can't have any content above 22kHz and is therefore not causing any audible IMD. And ...
B. Using a very low level, non noise-shaped (TPDF) dithered test signal (or finding a very low level segment in a music recording) and amplifying it massively, so that the dither is audible.
In case "A", although one could discern an audible difference, the result is actually backwards. The 24/192 version is reproduced with unwanted distortion, effectively at a LOWER fidelity than the 16/44 conversion! In case "B" we have created an artificial scenario that CANNOT exist when we're listening to music recordings, in practice it would massively overload a system, blow your drivers and/or ear drums, as explained in the OP. Furthermore, the difference with this artificial scenario is the audibility of TPDF dither noise, NOT a "much less harsh presentation".
If you really can "ABX a difference in these rates" at reasonable levels, then you MUST provide the evidence, because you are contradicting a significant body of established scientific evidence!
Rob Watts does apparently "know something about this". Unfortunately though he misrepresents/lies about it!! From your linked post:
1. Obviously that's nonsense. If -6dB is the max for DSD, then how can a noise problem (or anything else) occur beyond the max? If -6dB really were the max, every SACD would be unlistenable because the very highest peaks could only be 6dB above the noise floor and the majority of the recording would be below the noise floor! The actual noise floor (in the audible spectrum) of SACD is NOT -6dB, it's about -120dB, which is easily verifiable.
2. If the last one wasn't bad enough, this assertion is way beyond nonsense, it's utterly ridiculous! Consider that the theoretical limit of 24bit is -144dB but it's only in theory, in practice we can't achieve anywhere near that level because if 0dB is say the sound level of a truck driving past from about 10ft away, then -144dB would roughly be the sound level produced by two hydrogen atoms colliding! Of course, the sound of two hydrogen atoms colliding is way, way below the ability of speakers/drivers to reproduce and of the human ear drum to detect. So, talking about a real world signal at -144dB is very silly indeed BUT here's Rob Watts talking about a "-301 dB signal", which is roughly 100 million times lower than -144dB! So what's 100 million times more than "very silly indeed"?? The best I can come up with is "utterly ridiculous beyond imagination" which apparently, in Rob Watts marketing BS language, translates to "essential for the perception of sound stage"! It makes Monty Python seem entirely reasonable ... you've got to laugh!!!
3. And neither does an "off the shelf" $2 DAC chip with a standard linear phase filter!
3a. True but obviously you don't need more speed than a stock DAC chip.
3b. That's interesting, many/most pro audio ADC/DACs use 6 bit resolution at similarly high sample rates, I wonder why Rob Watts "cheaps out" with only 5 bits?
3c. Nonsense, of course you can dither a DSD system, if you couldn't all SACDs would be swamped with noise and un-listenable. It's true that you can't dither a 1bit DSD system adequately enough to linearise all quantisation distortion but you can reduce it to below audibility.
Sorry, but it's one of the oldest audiophile marketing tricks in the book: Take some issues that are inaudible, purely theoretical or miniscule to the point of laughable, FALSELY describe them as "massive and unique problems", explain how your new/super-duper DAC solves them and is therefore "massively" better than other DACs and worth it's MASSIVELY over-inflated price!!!
G