On Wed, Oct 22, 2014 at 5:39 AM, Vaclav Mach <vaclav.mach@artisys.aero> wrote:

we have a bad experience with Jack: we were running jack on a computer
with external and internal sound cards simultaneously. Jack was
complaining that there is no clock sync (since there is no clock sync
possibility on internal HDA / sound blaster sound cards).

sure, but this doesn't have anything to do with your current issue or the system design you are using.

JACK is perfectly capable of using any number of audio interfaces whether they are clock synced or not. It just isn't a good idea and isn't how a professional system would be built. It also isn't done by using the -P and -C arguments to the backend, because this doesn't do any resampling to keep the streams synchronized, but by using bridge clients like zita_a2j.