I had a similar situation one time when I had two sound cards. I had to disable the onboard to make it the add-on card work.
If you are using kde you might try the kde setup at Configure Your Computer > Hardware > Multimedia > Phonon and try to select a default there.
Desktop: AMD 3.6ghz X4, Gigabyte MB, 8GB ram, Multiple PCLOS's, 22.214.171.124-pclos3.pae.bfs
Server: Intel 3.4ghz X2, 4GB RAM, SATA, gnome2, *.pae.bfs, Headless, Servers: LAMP, FTP, Samba, Print, PXE, BT
HTPC: Phenom II X4 2.8ghz, 4GB Ram, 1TB SATA, PCLinuxOS-KDE, NVIDIA N220GT HDMI, *.pae.bfs