Two questions:
1) Do most/any/all of the above support USB input?
2) Depending on the 'media player', of course, can USB in principle handle any data rate/resolution/ format currently in use for digital audio?
I seriously don't understand all of the different sampling rates, resolution, etc. etc. out there today, not to mention the myriad of data file architecture options -- but I am interested in capabilities, I guess.
Most DACs these days even in the Doorway price point category will have a USB input.
The DAC's ability to handle various sample rate and bit depths via it's USB input will vary, although that too is fast becoming much more standardized as time goes by such that even the lesser expensive models now all tend to support at least 24-bit / 192 kHz sample rate for PCM files, and increasingly even the lesser priced models will support 32-bit / 384kHz for PCM, as well as 1-bit (bitstream)/2.8mHz for DSD, aka DSD64.
That above Pro-Ject unit is a good example (as are various models by iFi) of what is available at very reasonable prices compared to just 3-5 years ago. The Pro-Ject DAC Box S2+ allows the following playback:
• 32-bit / 768kHz PCM support (USB input)
• DSD64, DSD128 & DSD256 (USB input)
• Up to 24-bit/192kHz (optical & coax inputs)
Regarding the USB input, there are two classes of devices out there: USB Audio Class 1 (UAC1) which maxes out at 24-bit / 96 kHz file playback, and USB Audio Class 2 (UAC2) which allows for PCM and DSD file playback at the higher sample rates and bit depths mentioned above.
UAC1 can be well implemented and sound very good, but at this point is dated and limits/locks you in to no greater than 24/96. I would not buy a UAC1 limited DAC unless I had only CD quality (16-bit) files and no real interest in acquiring any hi-rez digital albums.
Since there is really little to no price difference between the two at this point, buying only a UAC2 compliant DAC is the way to go.
EDIT: There is also a 3rd class of USB operation now almost extinct, so-called adaptive mode, it was not very good sounding at all, and limited to 16-bit / 48kHz playback.