I spent some time AB testing the M3s vs some other DAPs in the same general price range. It seems that three chip families define the market at this price point; The Sabre series (9018/9023/9028), the Cirrus Logic (4398 and 43198), and the AK (4490,4490EQ,4495). All three families are very capable and while I think that implementation is far more important in the overall sound produced by the DAP than which chip is used, chip families due tend to have a house sound or tuning that tends to be visible in most of the products sporting the chip. I want to admit right up front, input quality, input processing, clock quality, and analog stages have a lot to do with sound and implementation is more critical than which chip is used in creating a quality product. Those other components may either enhance or mask the natural tendencies of the DAC making it harder to pick out which family is in use but with more samples of products with each chip, certain qualities do begin to show through.
AK (4490)– Good bass extension but slightly forward bass that extends into the mid-bass range, thinner mids, followed by slightly forward highs. Treble extension, while good, is not quite as well extended or controlled as the Sabre line. AK calls the line the Velvet Sound and I think this is a good description as when I think of velvet, I think smooth. The AKM series in general produces a very musical signature and is more forgiving of source material than either of the other families. The downside of the AKM tuning is, smooth musical rendering can hide detail and does especially when it is combined with the slightly thinned mids. For me, as a devote of blues-rock, guitar detail is all important and the AKM can sometimes mask it.
Sabre (9023) – Very accurate and clinical at the expense of being the most digital sounding of the three. If AK went for the “Velvet” signature, Sabre went with “technical”. Where AK went with natural, almost tube sounding filters, the Sabre series went for absolute precision sometimes at the expense of musicality. The Sabre series tends to have the brightest sound of the three families partially because it also has the best treble extension of the three (at times by a pronounced margin). The lows and mids of the Sabre series tend to be closer to neutral than the AKM series and slightly thinner.
Cirrus Logic (43198)– The CS chips tend to be a little closer to the Sabre than the AK in that they are slightly bass light with neutral mids and well extended highs. They are a bit thicker and fuller than the Sabre while still maintaining a clean sound and more detail than present in the AK chip. The CS provides a balance between the other two chips that offers some of the technical micro-detail of the Sabre while maintaining some of the musicality and natural tonality of the AK.
Again, these are the ramblings of an old fool so your mileage may vary.