Onboard Audo/Card @ Same Time

Would there be any sort of signal conflict in using a sound card and headphones for gaming but using an onboard audio spdif output to a reciever at other times?

yes , you can only use one audio device for one purpose like you can use ur pci for playback and ur onboard for recording or switch it back and fourth but you cant use the audio devices at the same time
hope this can help

Actually yes you can. I've ran onboard and a PCI card at the same time (though it was kinda useless). You just need drivers for both of the sound devices.