I've had the SMSL d300 for about 2 week now and I am happy with it. I haven't noticed any "burn in" FYI.
I upgraded to this unit as I need balanced outputs. I only use it with powered speakers with room mode EQ correction via REW.
I got this DAC for the ROHM chipset as I wanted a different flavor of sound than my ESS Sabre equipped Topping DX3+.
I would agree with most of the feedback online that this DAC is softer and more laid back than my Topping DX3+. Some people may call this "musical" or "warm" but others may think it is slightly less resolving than other DACs. YMMV.
Where I do think the SMSL d300 excels is the width of the soundstage; I am quite impressed with this aspect. My Topping DX3+ created a good soundstage between 10 and 2 O'clock, but with D300 is wider. Soundstage depth is roughly the same.
Cheers