I purchased the AIO card with the balanced analogue output cable and the AES digital cable.

I have a pair of closed back ATH-M50 headphones plugged into the headphone jack of the analogue breakout, which I believe are 38 ohms. I also have a pair of DT990 Pro 250 ohm cans, which are open backed.

Looking at the Hammerfall DSP settings for phones, there is High Gain, +4 dBu and -10dBV.

I read about the differences: +4dBu, it says for connecting to professional equipment like mixing desks; -10dBV is for consumer equipment like old stereos etc. This leaves the high gain setting, which to me is too loud when I use the M50s. Which one should I be using and why is there line level settings on the headphone jack?