Hello again! Thanks for all advices!
For the winamp solution. My winamp plays mods, but I just can't figure out how to make a wav from there. Anyway some mods sound different from the real thing.
The deliplayer is very nice actually as it does play these strange things in the lha's and lha's themselves too! The sound is still not quite authentic (robocod, lotus etc.). It tends to be smoother. Furthermore the wav recorder functions only for mono (shareware)!
My solution at last is still the analogue way...
As somebody here advised me, I made sure both comuters are equally grounded. And most importantly I plug off the cable tv-antenna from the tv(my amiga500 monitor)! That one made most of the noise.
There's still a little amount of noise there, but it's tolerable for me. I have also amplified the input signals within my soundcard +12 dB, so I can use more of the 16 bits of Wavelab.
This solution however requires that I actually have to play the game in order to get to a certain ingame music (lemmings!).
Thanks again, Pantofis