Driving amp with volume control from a headphone amp with volume control

[qec]

As the title states, I'm driving a SMSL SA-50 with a ifi Zen dac which is also a headphone amp. This means I have two volume controls. Guessing the headphone amp is sub 1v to a couple of volts. Question is: If I want the best sounds what is the generalization regarding settings of the volume knobs? Right now I have the Zen set at 1/3 and control the volume with the SMSL. Do most of the headphone amps do better when keeping away from max volume when it comes to distortion? Or should I be more concerned with the SMSL amp handling high or low input levels?

 

[Bob-23]

Generally, I'd go with a dac's line-out, as the headamps in dacs often are not very convincing.

 

[qec]

I will give that a go. Thanks!