Well, thanks everyone for the first round (I also took benefit from posts in debian-italian). Here is what I collected:
a) From 'lsof |grep /dev/dsp' it turned out that 'yiff' was using /dev/dsp. I removed it. Now KDE doesn't complain anymore but I still can't play sound neither in Gnome nor in KDE. b) Moreover, I tried playing an mp3 file with 'mpg123' under 'root' and I got 'Illegal Instruction'... Why? c) Many of you suggested to use es1370. Now 'modconf' don't let me remove neither es1371 nor soundcore. The same with 'modprobe -r' (of course). They say '... device busy'. From 'lsmod' it is seen that 'es1371' uses 'soundcore, but "who" uses es1371? Regarding "aumix" and OSS modules what are the critical things to check? Cheers, Cristian