Well, there's a recommended audio card
thread in another forum, but none of the posts specifically says they have working spdif... Hopefully someone will reply here.
As far as USB support goes, FreeBSD is using a new (and incompatible) USB stack for 8.0, so creating a USB driver for 7.0 series isn't that useful in the long run... However, the 4.1 versions in the source repository
have better support for FreeBSD - Device cloning for vmix (so every program can use /dev/dsp on FreeBSD rather than have to be set up to use a separate /dev/dspN for each)**, module parameters are now supported via the .conf files, and other enhancements. Basically it has been brought up to speed with the other platforms.
** Requires _FreeBSD_version >= 700111. PCBSD 7 and FreeBSD 7.1-RELEASE would be fine.