First of all, I am not a veteran listener, therefore you might say I am objectively worse at doing this comparison. To those who don't already know, these are purely subjective opinions.
I just had the Aune X1 over for a listen for a week. Comparing it to my X-Fi XtremeMusic on my Fidelio X1s, there is no difference large enough to justify the price tag. I suspect this being because of the low impedance, therefore eliminating the need for an amp.
The DAC on my XtremeMusic and the Aune X1 are similar, and even though soundstage is slightly wider and the sound a little more pleasing, I do not recommend what many users are recommending for the Fidelio X1.
Pink Floyd, even in 24 bit 96 khz SA-CD 3 mbit/s sound, sounds amazing regardless of which DAC/AMP is used.
What I do recommend for the Fidelio X1, is one of the HiFimeDIY DAC+amps such as the Sabre UX1 or maybe even give the higher output impedance U2 a try, since they are cheaper, have (according to some) better DACs and don't have a massive amp which does so little for the Fidelio X1s (not saying it doesn't need amping, but it doesn't need a amp so powerful it has to be turned down to 25%