The audio note transformer is one mod we don't offer but we have a better option if you feel it's needed. A Russian hand wound pure silver transformer of better spec. But this mod is not recommended and only makes the sound richer and able to run long runs of 50ft of aes cable. It's for 110 ohm and frankly no point to do it unless you really do have the need for a long run cable. Otherwise it's kind of pointless , this opinion from our designer and tuner. So we won't offer it simply due to us believing it doesn't give any benefit of sound quality improvement compared to cost. Take it as you will. But maybe for a studio situation and need to run cables across the way. Sure! The stock transformer is more neutral and natural imho. And sufficient for most people running shorter cables under 10ft or so. At least this partially my understanding for the transformer aes upgrade. For 110ohm.
Thanks for clearing things up!
I ordered my Spring from HK with everything sans the transformer because I primarily use toslink and USB.
Can't wait for it to arrive