Bug#510780: linux-image-2.6.24-1-486: sound card YMF-724F, firmware request failed
Installing the firmware is not enough,
the modul "soundcore.ko" is still necessary.
It would be fine to put some advice in the
kernel documentation or to fix the bug,
it is still present in version 2.6.26-12.
I published advice for Yamaha hardware: