Lampizator Amber 3

My understanding is in Amber 3 the Ecc99 is used in the gain stage, Ecc82 in the buffer stage, and the third tube is a 6X5 used in the rectification stage. In my Amber 1, they use Ecc81 in the gain stage. Other tubes are the same.
In my unit they had affixed labels showing the date codes in two places on the chassis, over the cover and the bottom plate, so removing the cover would break the labels. You should check with them before attempting to remove the cover to access the tubes since breaking the labels might void the warranty.
As others said, you should listen to the DAC and let it settle in before even considering replacement tubes. You will most probably keep it as is. No harm in getting an aftermarket power cord, of course.
Let us know how you like it.

Thank You All,
I tend to get a little over eager when anticipating a new component. After each read I was reminded of James Tanner's (Bryston) quote by his name on Audiocircle "Demo is Everything!".

For convenience I will provide Fred Ainsley's (Lampizator NA) response to a similar thread on Audiocircle: 
"We don't really encourage tube rolling in the Amber and certainly don't encourage the modification of our units. While you may be able to alter things in a way that you personally prefer, we believe the Amber to be voiced very well from the get go, shipping with quality tubes.

It is also difficult to support the opening of a sealed chassis without clearing it with us. This is unlike our "tube rollers paradise" or DHT series with external tube access.

I'd encourage you to give it a listen stick and contact us directly if there are tube issues or concerns.
Best,
Fred A."

Anybody know what a "listen stick" is?

My WAG is that it was a typo and he meant “stock”

Not sure if you still have the DAC, but the 12AU7 and the Jupiter coupling caps are the big limitations. They dumb down the sound in the analog system because the DAC is a slightly tweaked version, if not identical to the more expensive DACs. I forget which DACs had which "engines". The newer once supposedly have identical digital sections.

Anyway, it's your analog section that is doing harm to the sound, the digital section sounds awesome. The easy part is converting from the awful sounding 12AU7 to a 6SN7. On eBay there's a seller, garage1217, who makes nice adapters which will do the job. You won't be able to install the cover unless you put a hole in it for the 6SN7. An even more impressive improvement comes from bypassing the Jupiter coupling caps with VHAudio's .1uf ODAM caps, and even better results can be had by using the ODAMs, AND the CuTF V-Caps. 

What you love will be vastly improved. The veiled and smeared sound will be gone. The best easily obtained tubes, though you will have to hunt for them, are pre 1964 Soviet 6H8Cs. They are a direct substitute for 6SN7s. You can certainly use the many boutique Chinses varieties, most of which are not half bad.