so... X5 3rd has same dual DAC AK4490 chips as AK380($3500)?
It's understandable to find this confusing, since manufacturers have used the DAC chip has their major marketing tool for a while now. But in reality, they aren't as significant as one might think. Any of the "audiophile-grade" DACs over the last three years can sound as good, or better, than whichever one came out just last week, depending on their implementation/circuit architecture. Now a days they all do an amazing job rendering an honest recreation.
Why one DAP sounds better than another very often comes down to how much money the company invests in all the less marketable components. And of course, implementation, implementation, implementation. Utilizing the small real estate available in a DAP more efficiently than the other guy can win you the day.
Now, lets not kid ourselves. Astell&Kern products are overpriced. Everyone knows it. And yet, the fact they are overpriced does not mean there is no benefit to going with AK. They do offer more than FiiO does, generally speaking. Not only do find the sound better than any Cayin or FiiO product, even on my AK120ii, but the build quality is true luxury-tier. Cayin does a skillful job of faking luxury, much better than FiiO, but even they fall short of Astell&Kern. AK uses higher-grade materials, even in the chassis, because they know they'll make that money back 10-fold by pricing it as a "luxury item."
Not to mention, they offer SIGNIFICANTLY more Gigabytes of internal storage.
This is why I recommend folk buy used, if they're interested in Astell&Kern. It brings the price/performance ratio down to a more realistic level.