Sorry, I have lots of demands. It might not be easily attainable, but a good challenge just makes you better, no?
Better than Sony UI, and most clear, detailed, accurate, and natural sounding DAC/Amp section for iems(since iems(transparent ones) are very sensitive can pick up lots of nuances).
I'm sure the dual DACs are more of marketing than anything else, but most importantely, best implementation of course will reap best SQ. Fiio never fails in the output impedance department, but that's not everything to it, AK has great SQ with around 3-4ohms output impedance. Make the best deign judgement, if you think it needs multiple channels for DAC, use one, like the 9018, if you think it's the same for mobile interms of performance, with power savings, that's fine. I've been liking ESS sound lately, not sure if it has more to do with implementation as AK uses 2 Wolfsons and they sound great.
It would be nice to use it as desktop DAC(with line-out to a nice amp for the desktop rig), and nice quality internal amp implementation for clean sound for very transparent iems.
I personally think, no need to put in an extemely high power amp as people with power hungry over-ears should get a dedicated amp to connect to the DAP, but for portable over-ears, it makes sense to power them adequately.
I have high faith in you Fiio, and you can do it.