I've noticed I actually had not reported this here, but thanks to Bill-P, I had given the Sonic Frontiers TransDAC a try with the HE-560.
Well, for me that initially needed a "oomph" for these headphones, I wasn't disappointed.
I usually only hear subtle (not say non-meaningful, or course) differences between the different audio pieces I tried outside of headphones, although keep in mind I haven't tried that much - especially costly systems. But I was stunned by how much difference one DAC from another could make all of a sudden (I was using either an ODAC or Gamma2 before).
Bill-P had been raving about his TransDAC, even selling it's 1k+ Neko once its TransDAC had been paired with antijitter stuff, and I can only support him. It's been nothing but great with the HE-560, and for my other headphones as well.
Given the price point of this vintage DAC, I would urge anyone to at least give it a try if you happen to find one.