The normal version is working in ACSS current mode and is tuned for a neutral sound signature, SA version works in diamond differential and does not use ACSS nor ACSS cables, instead has only RCA and XLR input/output and is tuned for a "musical" sound signature. I don't have any experience with their diamond differential musical dac's and amp's, but from what I read, it is possibly something like "neutral, but slightly sweet" (google translation of audio-gd's chinese sound flavor page), the mild degree of coloration mainly noticeable on piano and violin but makes vocals more enjoyable. Speculation on my part.
Some people may strive for the most honest reproduction and any coloration is undesirable, but there's some people who would not mind a little coloration if it can make the music more enjoyable.