Interesting, my system is all Cardas but never bothered with the headphones. Mine are 650’s as well, I guess I will look at getting a set
Sennhieser 650's
..using a dedicated balanced headphone amp. The upgraded Cardas cable had a drooping shrink wrap so it went back to Cardas for a no charge fix. In the interim, I plugged in the standard issue cables that came with it. I don't know if the very obvious increase in fidelity was the Cardas, or that the phones are used balanced.....but there is a holy cow difference for the better with the Cardas.... Funny that Cardas isn't my cable of choice for the rest of the system.