I have an Audio Attenuation Cable Adapter made for IEMs from Ebay that can select 120, 200, & 300ohm impedance.
I have been using the Crack (non-speedball) with this cable, but I'm not sure if it is safe to do so. Will I damage the amp, tubes or the headphone by doing so?
The audio sound quality is much better with the adapter than without it. I normally use my HD600 straight to the Crack, but the AKG Q701 is really fun with the Crack.
Flow Diagram:
Dac + Pre-amp (Resonessence Herus+) -> Crack -> Audio Attenuation Cable Adapter @300 ohms -> AKG Q701(62 ohms)