Yes, I have.
Both sound good, but they are definitely different sounding.
Onkyo, more detailed, analytical, less warm. More depth in 3d soundstage.
X5iii more musical, warmer, somewhat less detail, very immersive but 'intimate' soundstage. Excellent separation/location of instruments and voices in 2 dimensions
I thought balanced made a bigger difference on the Onkyo than FiiO -- specifically in terms of soundstage, and also, a bit tighter bass.
Sound sig and stage size are the biggest SQ differences.
I like the feel of the FiiO in hand better -- preferred the smaller width/height and didn't mind slightly greater depth. Also preferred the rounded corners of FiiO vs sharp pointy corners of Onkyo.
Don't know if you run the risk of the 'loose headphone jack' issue with a new dp-x1. Seemed like a serious problem, especially if it crops up after end of warranty period. As much as anything else, that drove me away from the dp-x1.
I can't really say much in comparing the usability of Android or streaming apps. Neither was a problem for me to use, and I didn't notice anything remarkably good or bad about that with either player..
Hope this helps.