GeForce GL 710 (GK208) and nvidia 375.66, Fedora 25 x86_64
Fortunately, it appears that the onboard audio was disabled in the BIOS.
I didn't knowingly make any changes there during the videocard
replacement. Now, in mythtv, I can select from vga or hdmi display,
with audio through either set of speakers. vlc starts with audio
visualisation active but the audio device selector works. SMplayer
shows a shorter list that doesn't include the active hdmi audio
subdevice. I'm not yet confident in predicting where all the active
windows will appear :-)
John P