Typically a single audio jack domain is sufficient. The default domain is called “default” (jackd -n default). By default all applications connect to the “default” Jack domain directly with Jack API or with an ASIO (Windows) or CoreAudio (OSX) driver.
In the case of a second Jack domain (jackd -n default2) how can Ardour be connected to the secondary domain?
This question applies to the various platforms (Linux, Windows and OSX).