The sc46xx driver has been removed
due to copyright issues. The last kernel version that had this module included was 2.6.22.
make sure you have the linux-headers package installed. Then download the original alsa-driver tarball, unpack it, cd into the directory that creates and:
./configure --with-cards=cs46xx --with-sequencer=yes --with-isapnp=no --disable-verbose-printk
By now there may be a package to add such removed drivers.