The sound is good to the price as is, but with a few modifications, it can compete with DACs costing several times this little gem.
I recommend a little soldering for best results.
You can power it from a Raspberry Pi or the like, in which case you should only connect ONE gnd or else you might end up with a noisy ground-loop. I would recommend a CLEAN 5V supply instead (USB battery power banks proves to be good and stable low-noise power supplies).
I also recommend to keep the I2S-cables as short as possible to avoid picking up noise. This results in a cleaner digital signal with less error-correction (jitter), hence a better sound.
If you have the nerve to solder directly onto the SMD components, you could do my modifications AT YOUR OWN RISK. I have more than 30 years of soldering experience. Keep in mind, you could easily fry the board instead …
YOU HAVE BEEN WARNED!!!
All modifications are done AT YOUR OWN RISK, and I take NO responsibility for destroyed boards!
I soldered small capacitors (8,2nF, though other values might prove better) directly onto the SMD-mounted DAC- and XO-chips. Especially the XO-mod made a huge audible difference. The impact of the DAC-mod is a smaller, but still gives a significant improvement to the sound.
I have deliberately NOT pointed out which pins to solder, as you would need a good knowledge of CMOS and SMD-circuits before even switching on your soldering iron, unless you deliberately want to burn your board instantly.
Specs for the SMD-chips, along with following the PCB and using a voltmeter, would lead to finding the right pins in minutes or seconds.
The unmodified board sounds fine, however the modified version is in a totally different league.