Where are you seeing any firmware update? And even if you found one, what is the confidence that it would not brick the unit? Company doesn't even have an ecommerce system. No way I would install any executable from them anyway on my machine to upgrade said firmware.
Link to firmware with hard to read manuals
http://www.audio-gd.com/Products-EN.htm
As far as I know the first few revison for the FPGA design now at least 13 years in the making and used in several of their late products where sourced outside Audio-GD. In later revision I wonder if not Kingwa where more involved in the development. And late produktion I'm told had a complete rewrite which they now can disdribute from their site. Older version they would only install from a remote desktop session at a resonable fee.
My first encounter with this FPGA design where the DAC-19 DSP revision in 2010 (released some time before this). DAC-19 first started out utelizing a standard S/PDIF receiver (testet somewhere on this site) and later got an FPGA from its bigger siblings just before they desided saving the sparce PCM chips for the Masters. DAC-19 PCM take the same firmware files as the M7.
Anyway, their mail-support have always got me sorted when in doubd — even for 7 years old second hand products. Witch few other DAC manufactores can claim. RME is the only one that comes to mind.
Still I prefer the sound from my M7 in 8xOS mode (not Singularity revision) over any of my RME DAC's in current hi-fi setup. For some reason it let me focus on the music over detailed and what apears as flatter 'sounds' comming from RME. Had both RME and M7 up for a several months with identical digital transports and always ended up on the M7.
For direct factory sale to end user 300 hour burn in at factory before testing and shipping seem a good idea given cost of return shipping if fault accumulate
Probebly does nada for the sound after warm-up but marketing have a free selling point for those whom are in believe.
There are only two adjustment points for each audio channel inside this design. Sugesting all the discrete circuits probebly have some accuracy issues that adds to caracter. I doubd I can hear the difference from .008% and .003% distortion figures for the two channels even if this difference would look nicer if aligned.
Although, the nonlinearity intrigue me. Given Kingwa comes from amp building (
cloning Krell is the saying) and should know his stuff this beavior makes one wonder if the design is dated and not been adjusted for newer replacement components like new transistors etc. The M7 design have been taken in and out of production over a decade when stock of PCM1704-K chips have allowed for short runs.
One interesting test would be if verify if it actually has the K revision of the DAC chip. Or if they are reprinted U versjons.