I can use both my integrated or PCI audio as an output with a few clicks of a mouse. This is what I did:
OS = XP. Soundblaster PCI card and nvidia chipset with soundmax driver integrated audio.
Assuming you have integrated audio working ok, install the PCI audio card and power up.
Let windows find the device driver (don't install any extra s/w yet). This will probably cause the integrated audio to "dissapear", but don't worry. At least you can see the new card in "sounds & audio devices" under control panel.
Reboot the PC an go in to the BIOS. disable the PCI audio entry that is now in there, save the change and exit BIOS.
Open"sounds & audio devices". Under the audio tab you wil see both cards as a drop down in the "sound playback" field.
To test, move your speakers from one port to the other to match the selection in "sounds & audio devices".
If you have two lots of speakers (I use direct speakers off my PCI card and my TV with my integrated cards for when I do TV Out. So you can just use "sounds & audio devices" to switch between the two.
Load any audio s/w as you see fit and run some selection tests again.