I wanted to say, that in Multibit dacs you hear the sound as one unique, flow. In Delta Sigma it has some portions: here is bass, here is tremble and it doesn't have any connection with each other. But in Case of Multibit. The sound is like a huge Flow. And i like it :)

And this Graphic is not the most important thing, when you speak about real SQ.

Yes, I agree, that 801 lacks a bit at high freq, but the mount of details is still the same, like in dx100 or 901. but the whole sound impression is so, that it sounds a lot more fuller. It sounds "massively", like some really "big" DACs. Because of Multibit dac.

Because Sabre sounds very synthetic. Compare old-school 801 and DX100. The first one sounds fuller and deeper.

I would like to have a replaceable battery, but! It mustn't be easily replaceble! I would suggest not to use glue at least. So, that it it could be replaced by a master.

Actually Sabre Dac is not the best solution for DAPs. I would take a look at PCMs or AKMs.

The amp section must fit ciems. A lot of power is good, but not always. Focus on the quality, not power. Something like E12 IEM version would be acceptable.

Oh, and the last one. MUSTHAVE! HARDWARE BUTTONS to control the music.

And the last one. Top players use Sabre: 901, Dx100... I would like FiiO to make a DAP with a Multibit Dac, like 801. That would be much better, because you made X5 with pcm1792 ( one of the best delta-sigma dacs imho, better only ak4399 i guess) and it sounds a lot better (for me) than Dx90 on...

Easy modification: something like plate-amps by HfMan.