Thanks.
I have indeed a memory of out-of-the-box fit with a Macbook, keys,
connections and everything. Only, the user wanted a jukebox and the sound was
almost inaudible. Because there are two standards for combo jack connectors:
the universal standard, and the Apple standard. Everything else was working
fine so I flew back to my place with the laptop and kept searching until I
found some nice drawing about the jack standards.
I only needed to play wit the pin configuration of the soundcard and switch
the base channel for the mic channel. Another option would have been to
invest in a $2 adapter but my friend was too greedy for that so we went for
the soft way.