I'll have an X5iii in hand tomorrow and I'll post something. Not very rigorous, since I don't have the Onkyo in hand any more, but at least some impressions.
Then more later, once I get the Fiio burned in.
I've had my X5iii for a week now. I like it very much, more than I expected. Probably halfway burnt in, since I've left it looping when I wasn't listening.
I agree with most of the other impressions/reviews. Very 'musical', yet still detailed, with
great instrument resolution/localization. My only complaint is that the sound stage seems small.
In comparing X5 to the dp-x1, I would say the dp-x1 is more analytical and a bit more detailed, with a larger sound stage in all three dimensions. Sound signature is not that different, but the dp-x1 seemed a little cooler (vs warmer for X5), with more energy at the high end (more sparkle?). Bass impact and extension comparable, with more mid-bass energy from X5. But the tonality differences subtle.
Overall, I'd say both are very capable DAPs, and if the Onkyo was at/around the same price, it would come down to your listening preferences. As the price differential is near 150 USD, I would (and did) have no problem picking the X5.
In 'slotting' the X5 with the other DAPs I've tried, (dx80, Plenue M2, Opus#1, dp-x1) I'd say the X5 comes closest to the Opus. Opus probably a shade less warm, slightly brighter, maybe a bit more detailed, with a somewhat larger sound stage.
To compare sound stage:
X5 -- onstage with band
Opus -- front row at club
dp-x1 -- 5th row at concert
Please consider that I'm comparing the sound of the X5 in my ears to the sounds of the other DAPs in my memory.
BTW, most of my listening (to all these DAPs) have been with the iBasso IT03s balanced with an ALO Audio Tinsel cable. I've been avoiding my CIEMs (mostly) since I need to tweak the sound to get to my preferred signature (a little bass boost with Frogbeats C5, a little treble boost with Aurisonics AS-2). IT03s are right there out of the box.
Bottom line, X5iii is a keeper. I'm sure I'll eventually pick up a dx200 (once the beta test is over) and then we'll see ... perhaps some other HeadFier will get a good deal on a lightly used X5iii. :veryevil: