I'm sorry to spam but this finally unravels the mistery.
I realize that if you install the package


two volume control applets will be built: volume and volumealsa

volumealsa works out of the box, for volume instead you need

1) sudo modprobe snd-mixer-oss
2) lxpanelctl restart

and it works.

to load the kernel module at boot edit "/etc/modules" and add snd-mixer-oss at the bottom.