I believe mine is a Mk. 1.5
the difference between Mk. 1 is 2TB SSD storage instead of HDD, quieter internal fan, different back plate to incldue different antena positions and USB 3 for backup/additional storage attach. More system memory too. I don’t know if any electronics have changed or been updated.
I had the Mk. 1 in my system for a good few weeks prior to getting mine straight from the factory direct. I listened for many hours too. The main difference is that mine is dead silent, zero vibration and does not run as hot as Mk. 1 Also, boot-up time from standby is much faster too.
it just produces wonderful music in my living room and the instruments sound soooo real

I can listen for days on-end without any fatigue whatsoever

to be honest I’d love to hear some of the newer high-end Streamer/Dac combinations just to compare the sound signature to my system.