Have been working with Ardour lately and the multiple audio devices (internal + PCI) have been causing issues both on output and input. The easiest workaround is removing totally the unused sound card, which in my case was the internal Intel HDA. The single step required was to blacklist the module of the sound card. You can identify the module by “lspci” and then blacklisting the module is straight forward:
and add the line
blacklist <module name>
A single reboot should do the job or you could unload the module instantly. Although, reboot would confirm whether the blacklist function worked or not.