I upgraded to the Master 7 by replacing the digital board in my 7.1, so I can only compare to my set-up with the Calyx DAC, which I did before the upgrade. I had Audiophilleo feeding the 7.1 and then daisy-chained it (since two of the inputs were connected together) to the Calyx DAC. I felt the Calyx, fed by the AP1/PP was a tiny bit more detailed and, either in a quick A/B or longer listening, made music more "young" sounding as Kingwa described, and the 7.1 was "darker". Upgrading the digital board seems to have my one, tiny disagreement with the sound of the 7.1, where I felt it was a very tiny bit lacking in most areas, but those tiny bits made me want to listen with the Calyx/AP1/PP/Vaunix combo more often.
To explain some of my feeling -- back when I bought the Metrum Octave, initially it had this amazing, extremely lively presentation where it emphasised even the quietest sounds in the music. It was addictive to listen with. Then it mellowed and became more boring (if still very natural-sounding with the usually difficult-to-reproduce piano and violin).
The Master 7 is more like the Octave was before burn-in, but without the usual sacrifice of a NOS DAC, which can be too mellow in some cases. On the other hand, the Calyx DAC is, used by itself connected via USB direct to my computer and using no other power source, sounds technically great but very "digital" and unnatural. Using a good source via the S/PDIF input (at least the Audio-gd DI but better still with the Audiphilleo set-up) the Calyx was just about spot-on.
The Master 7, however, has a combination of the "clear" sound of a Sabre DAC (eg: The Calyx) + the organic naturalness of a NOS DAC + the liveliness of the Metrum when new. In other words, I don't feel like I'm missing any of the other DACs I've owned or own using it, which I did very slightly when I had the Reference 7.1.
I haven't done a comprehensive comparison of the USB32 with the Audiophilleo set-up, but it's pretty good, if not quite as clear-sounding (but at a much greater total cost the AP set-up should be better).