been using the master9 for more than 1 week i must say this is the best amp that i have ever heard with HD800, i had been always disappointed and wanted to sell the hd800 from the 1st day i got it, have tried many amps,namely firestone bobby, zana deux, burson conductor, decware csp2+, agd sa31.., upgrade cable to make it sing but most did not work. IMO, the decware with very specified tubes set can partially show the 800 potential, and some how the zana deux but thats it , still cant stand more than 30mins with hd800. Everytime i put in on my head, theres always feeling that the singers were trying to "spell the word" instead of singing, thus most of the time i kept using my lovely HE500 T__T
The master 9 is another story, in short, it makes the HD800 sings. Sound is beautiful, smooth, effortless and very euphoric just like very good tube amp, while maintaining all the strength such clarity, 3D sense, sound stage and instrument separation, further enhancing bass extension, more than satisfied rumble sub bass and very high treble extension without any hint of sib. This is the first time i understand what wire-with-gain and transparent power really are.
best money i have ever spent since i joined this community ^___^
btw, im using it with m7 via custom sofc teflon acss cables :)