I got the BOSS about 10 days ago and have been 'testing' it out with my Dali Zensors powered by Marantz PM5005.
The BOSS is mounted on a Raspberry Pi 3 and the combination sounds pretty good to me. Overall I am very satisfied.
I do not have an expensive power supply for my RPI - just a normal Motorola charger for which the RPI has never complained.
My source is all digital - mostly FLAC files and also some online radio with bitrates varying from ~40 kbps to 320 kbps.
Some of the low bit rate radio stations also sound quite good to me.
This afternoon, I did a comparison (side-by-side) between this DAC and my FiiO D03K DAC which is connected to my Panasonic Plasma smart TV.
Only on a side by side comparison you can make the difference out.
After listening to various genres of music I could say that the BOSS tends to somehow bump up the lows and the highs.
(I am aware of the 'burn-in' time of about 50 hours - which I have not yet crossed with my BOSS - so I might come back with my observations after some time again)
I do not know if this is called the 'dynamic range', but if yes, then that is higher/ wider.
So, for casual listening the BOSS tends to make the music sound 'punchier'. However the FiiO which costs me half, give a much flatter output. This seems to be better when listening to vocals.
The low end 'thump' is significantly higher with the BOSS - you can really feel that. On the flip side, this sometimes tends to overpower the vocals.
I have not had any experience with other RPI DAC's so, I cannot comment on that part.
Currently using Volumio but waiting to try MoOde.