Been a bit since i have looked at this thread... seems it devolved into a arguments of opinions for a bit...again... lol.
I will say, that the Q 5K has been the best small portable BT DAC i have come across. It is quality sound and software.
I have used Fiio products, and have had nothing but issues, failed hardware, defects, quality control issues etc. The main issues though, terrible firmware and apps.
Qudelix is light-years ahead in firmware and software development and stability than Fiio, imo.
Fiio products physically feel premium in build, but are extremely lacking in firmware and app maturity and quality.
However, in customer support, in my experience, Qudelix lack in basic friendliness and communication skills. They blame the user first, and say they know better and are very standoffish and defensive when any user gives a suggestion or trys to explain their use case or feature request.
(Fiio, they just gave me the never ending run around when i needed support, copy paste very poor English response, and never directly addressed my issues nor issued me a rma)
I have 3x Qudelix 5K's. One was plugged into power for a few years and was my connection from my Apple TV 4K to my desktop speaker set, for my TV/movie watching etc. One was for use with my main full-sized headphones(SkullCandy Crusher Evo) and one for my earbuds(various) and occasionally connected to my ipad via usb c. Have zero issues with any of them. The software (app or browser extension) has been amazing! The EQ is amazing! The sound, after much time tweaking EQ, amazing!.
However, i ended up changing up my audio/media setup(too much to explain) and ended up retiring the 5K's. I have since switched to using a Fosi Audio Q5 Pro DAC and source input of Optical from my new Samsung tv's toslink out. This powers both my speaker set, and is great for headphones. It only has physical knobs for manual (analog) adjustment of Bass/Treble, no EQ, but i find i do not need the fancy EQ of the Q 5K, in most situations now. (my hearing also has changed, as i get older, or cause i was stupid and caused myself some hearing damage...long story... )
I must say though, Fosi Audio, is a EXCELLENT company. Very willing to communicate with their users and discus future products and feature enhancements etc. Even inviting many to their invite only "Product Development" group and is slowly allowing for beta testing of products. They are not really in the "portable DAC" market, focusing more on amps and pre-amps, and desktop style DACs. Nor do they have any app controlled DACs, yet. But they seem to be interested into getting into this market, or at least expanding their product offerings. I would suggest keeping an eye on them and check out what products they do offer, if they suit your needs.
As for my Quidelix 5k's.... may sell 2 of them, and keep one. But am a bit lazy havn't touched my ebay account in years...
TLDR: Moved on from the Qudelix 5K. It still a great portable DAC, best BT DAC i have owned...