Both units are way past the threshold of audibility where noise and distortion is concerned. The choice should come down to factors such as functionality, connectivity, reliability and aesthetics. Personally, I would rate the PEQ capability of the DX5 II over the supposedly better DAC IC in the SMSL.
I don't own any SMSL products (I have been close to purchasing some in the past), but I do own a Topping A50s/D50s/P50 stack, and EX5 and the DX5 II that arrived yesterday. I've had no issues with any of them (I appreciate that it's early days with the DX5 II!).
Gratuitous shot of my new DX5 II on my desk

...
View attachment 467937