Differences between old Audio Note DAC1 and DAC3

[barnamax]

Hi all,

I'm quite new of this community, although I need your help because I'm in a doubt about my DAC Audio Note DAC1.
It is the old model, that one equipped with the BB PCM63 dacs, and it has received several upgrades during its life. Now I would like to improve again its performances and I wonder if transformes between converter and the valve output could be a good target.
DAC1 uses only 3 transformers when DAc2, DAc3 and bigger brothers use 4 transformers called respectevly TX1, TX2, TX3 and TX4.
I would like to install in my DAC1 components used in DAc3, but I didn't find any information...where mat I buy these components? Audio Note Italy doesn't answer....could you help me?
Further suggestion about improvements?
thanks a lot, have a nice day!
happy listening

Massimo (from Italy)