Hi coot,
My setup is the following:
MacBook Air -> Oyaide Continental 5S -> DAC-2 DSDse -> Acoustic Revive Line-1.0xs -> ST-500 MKII -> QED XT-350 -> Dynaudio Focus 260.
All power cables are stock cables so far.
The break-in time is about 40-50 hours now and what I can say is that right out of the box sound of ST-500 MKII could be considered as thin or lean and etc. but it changed quite fast toward full bodied bass. I'm still waiting for 200-400 hours and will share detailed report but now I don't have any lack of bass or issues with other departments. Sound is keep changing.
Will be happy to answer any your questions.
Evgeny