Hello I own a Amber 3 and have modded it with premium caps, Belleson regulators tube upgrades
And the New Synergistic Orange 3.1amp Slow fuse a nice upgrade to a very good dac.
You cannot use 12Bh7 , it isnot a drop in replacement my friend is a 40 year vacuum tube amp- preamp designer,builder. Power supplies may be totally different , the Ma, transaconductance is different .
He didnot recommend it so I didnot want to disturb the circuit. The 12au7 you can upgrade
It comes with a ok Phillips late 70s early 80s . Mazda make some nice ones or older hollandAmperex since you only need one $150 for a good one ,and the Synergistic tube for sure .
I just bought the hot usb cable from Serbia that they use in the a Pacific it is around $850 retail
But Very natural better then anything under $1k +for sure and a great power cord is a must if you want to get the most outof it .Ask Rob . Triode Audio cables makes a killer digital 10:cable for $450 with the upgraded a Furutech connectors , just replacing fuse,12au7 tube, power cord , and usb cable will make a Huge difference
Across the board.