If you get the X3, you don't need an E17, as the X3 already has an amp built in and can drive almost anything.
I just A/Bed a bit. See picture for the setup.
I used a Beyerdynamic DT770 Limited Edition 32 Ohm, Sennheiser Momentum over ear, Beyerdynamic T90.
Put the same songs on both players, matched the volume. No EQ, DX50 (1.2.8) on middle gain, X3 (3.0) on low gain.
I started the songs on the same time, so I could just turn the knob on my Fiio Headphone output switcher (HS2) to seamlessly switch between the two sources.
Soundstage - no difference between the two
Highs - bit more present on the DX50
Mids - both nice and present
Lows - slight, very slight advantage for the X3, much less than I expected.
So the DX50 is a tiny bit less present in the lows. I honestly didn't expect the differences to be that small. Before I had the headphone switcher, I re-plugged the headphones and the additional time plugging and re-plugging made all the difference in my ears. Much more "perceived" difference. Realtime switching with properly matched volumes showed me that these two sound very similar. I really had to concentrate hard to hear any difference in the beginning, then some specific areas in songs became clearer.
Result for me:
whichever you buy, you won't be disappointed. With a headphone that needs lots of power to awaken the bass (T90) however, you will be happier with the X3.
Then I connected my Bravo Ocean and the Bottlehead Crack to the T90 and boom, there was bass a plenty (but that's another story).
I can only recommend a setup where you can play for both sources/DACs/amps simultaneously and in realtime between them. It makes a lot of difference, as your memory (even short term) is otherwise playing tricks on you....
I really can't decide between these two players. So I would be happy if somebody could call answer me some questions.
1) Which player has more power? (Maybe i gonna plug in my 250Ohms Beyerdynamics) Can both players handle it?
2) How does the EQ of the iBasso?Is it usefull or it just destroy the whole sound quality? I know the FiiO has no EQ, but a Hardware Bass and Treble adjustment. Is it better than iBassos 8-Band EQ?
I would be really happy if somebody could answer me that questions.
If you care... the UI on the X3 is unbelivably BAD. Even the most recent update hasn't really done a whole lot. It sounds great. BUt I still prefer my rockboxed gigabeat DAP just for the interface (and it's the best sounding non 24 bit DAP in my mind) ......
When I switch over to 24bit tracks the difference is huge... but the Interface on the X3 drives me NUTS!!! I've been looking into the IBASSO just to get rid of the X3... so if you buy an IBASSO and want to trade let me know.
That said, I'm waiting to see what happenes with PONO before my next upgrade.
The X3 interface with the latest firmware and the custom list-based mod posted on this forum isn't too bad. I mean, it's not great or anything, but it's useable without being annoying to me. I actually returned the first X3 I bought when they came out because of the UI, but I can live with it now.
I hope that in your comparisons, you volume matched the sources with identical music files on each.
Gonna have to disagree with your point entirely that the latest DX-50 firmware (this being 1.5) goes towards emphasizing sibilance, I really do not detect this at all. Sibilance is a problem of matching a vocalist with a vocal recording chain. Once the sibilance is there on the recording the only way to make it less apparent is a deesser or very careful sidecahin EQ. DX-50 1.5 firmware does not emphasize, boost, bring forward any area of sibilance in a recording exhibiting this.
The latest DX-50 firmware has increased the apparent presentation of the sub fequency content shelving up throught the lower frequencies and improved on all other areas compared with 1.2.8
On accurate IEMs like the Etymotic ER-4s this results in a very pleasing, detailed, rich, present and engaging portrayel (all the qualities you state for the AK100) . The highs frequency content is all there and in no way harsh or unpleasant, I agree with your statement that the soundstage is very good.
Regarding bass accuracy, you can still hear the quality and detail of instrumentation in the LF and with the new firmwares increased apperent bass you just get more of it.
the two firmwares leading the pack for sound on the DX-50 at the moment are:
Factory Stock firmware 1.5
Doc2008 Mega Sound Explosion Second Edition custom firmware (and first edition)