a shot of the internals for anyone who wanted to see. this thing is quite well put together, the case is actually all metal, and then shiny acrylic sandwiches it on top bottom and front and back only the sides are still metal. the construction is solid otherwise, took me ages to disassemble it completely as i'm rather cautious of breaking anything
i've only had a z-audio mu (battery powered portable) before this so i don't have a lot to compare it to, but i can definitely say the original master is a significant improvement. the amp initially was a little harsh on the highs the mids were smooth and the bass didn't go too low, this is all relative to the mu which is quite a warm amp and a little bass heavy.
anyway, after using it for a while (1 week or so) the highs seems to have become more bearable and the mids are still smooth as but bass is nicer now and goes down low like i'm used to.
the amp is a lot more detailed than the mu and seems like its frequency range goes higher to and so using them on my MS-1s is a little tiresome sometimes i think i just need my ears to adjust on this headphone, but on my DT770 Pro/80 and my ATH-AD700s it's much better and especially smooth vocals with the AD700s. The bass with the 770s is good, but i think that this may be more due to the headphones, but in either case it matches well.
just for kicks i attached the 1/8" to 1/4" jack from my MS-1s to my KSC-75 and had a listen it was actually quite enjoyable, but like the MS-1s the highs are be a bit fatiguing