This is sound and well reasoned advice. You speak to the virtues of A+ for those using Mac-based systems. For those with Windows-based systems, HQPlayer is the counterpart (although HQP also plays on Macs). I know that Esoteric has done a huge amount of work on its own internal upsampling process and that may be a significant part of your great sound. But for many, if not most, other DACs the ability to upsample to high rate PCM (for Chord DACs and some others) to DSD 256 or 512 (for most other DACS) creates the possibility of using better filtering tools than are used in the DACs themselves. Roon now offers that capability in Roon, but most HQPlayer users feel that the different filter choices afforded in that program best allow us to fine tune the sound of our DACs to their highest level. Like Roon, HQPlayer also seems to benefit from putting its core on a very high powered computer and then using an NAA (network audio appliance) as the simpler, cleaner device connected to the DAC. Because of that neither Roon nor HQPlayer do what A+ does in optimizing computer system processes to reduce noise. There are, however, Windows optimizer solutions that some claim do improve sound by reducing system noise even in the main computer.
The other confusion worth addressing is that people confuse upsampling with hi-res original files and assume that the benefits of both can only occur at frequencies near or above 20kHz. That misses the point. Upsampling doesn’t recreate data that wasn’t in the original (say 16/44) file. What it does do is to allow the impact that the D-to-A conversion process has on the original to be moved further away from the audible range (so that any artifacts of that process are well beyond 20kHz) AND it allows the use of filters that introduce less pre-and-post ringing and less destruction of time-correct data than if those filters are applied to a 16/44 file directly. If poor filtering was used in creating the 16/44 file in the first place then much of that damage may already have been done (and that is why some of us buy hi-res original files because they at least imply care in handling in this regard). So the reason that upsampling matters in the audible range between 20Hz and 20kHz is that it prevents (as much as possible) artifacts of the D-to-A conversion process from spilling down into those frequencies.