i got the answer for my question from B&W (regarding jack output power)
16 Ohm minimal impedance
not bad at all.
I'm owning MM-1 since 2010 and I'm very happy with them. Amazing sound form those little speakers.
I was amazed with them because in 2010 I owned NAD 325 + NAD 525 with Acustic Energy neon 1 (I think they were called like that) and my impression was that MM-1 are better. Really.
More details, more stereo separation, more space. Of course they couldn't compare to NAD power and bigger AE speakers but I liked more to listen to them then to the full NAD/AE hifi set.
Now days, I have better hifi setup and also top headphones so I looked at them in a different way but still I like to use them.
For example right now I'm listening to them trough portable headphone output with B&W P5 headphones and they sound very good. Running iTunes with apple lossless.
I tried them with senheisser HD650 (300ohms) and they had problem to drive them properly but still it was not bad. Anyway I think the output is much better for low impedance headphones like B&W P5.
Remember to use them in rather small room. They can kick you then :)