Impedance on the headphone out on the C.A.B

Hi everyone. Anyone know what the impedance on the headphones out jack? I have noticed that when I plug the headphones in the headphones out on the torpedo cab, the volume is rather high and there is a bit more harshness and some fizz to the tone. But when I plug the lineout to my soundcard or mixerconsol the volume drops and is a lot smoother. And when I crank the volume up the smoothness is still there and the tone is really good. But when I plug my headphones back directly into the cab the sound is more fizzy and somewhat hard. I Plugged both the lineout and headphones out to my soundcard to compare them and the headphones out is a tad bit louder and more gritty. I Have a few different typ of headphones from 80 Ohm to 300 Ohm and there is no real difference in volume or quality between them when using them with the cab. I'm thinking the headphones out is best used with headphones with high impedance due to the high volume. I am gonna do some more test lowering the volume when playing through the headphones from the cab and raising the volume when going through the mixer, but have anyone else noticed that the tone is more gritty and with some more fizz?