Thanks for your advice and suggestions, Agoldnear.
Do you have all other applications shut-down that may be using one or all of the components in you system?. Yes
Why did you not create an aggregate device with the miniDSP and the DAC/HPA set-up? This is what I did. The miniDSP is on the USB output; the DAC/HPA is on the built-in optical output.
Did you assign the different device outputs to the same two-channel (L/R) audio streams? I’m fairly new to Audio MIDI Setup and don’t know see where I would configure that. The multi-output device I created works as expected—except with Audirvana, of course. Does that indicate the audio streams are assigned correctly in the aggregate device?
In Audio MIDI Setup, I found that my two devices were set to different sampling rates, so I set the built-in output to be the same as the miniDSP Flex. Then I went through the process involving restarting the system and allowing it to resync exactly as you suggested.
The result was the same, except for an odd situation that is not relevant to my purpose— distortion in Tidal playback through the aggregate device that was not present in previous trials. The following “table” summarizes the results, with the first line being the table header.
Application; Multi-Output Device result; Aggregate Device result:
Apple Music; Sound via both outputs; Sound only via first device added
Tidal; Sound via both outputs; Sound, distorted, only via first device added
Audirvana 3.5; Error message; Error message
I have found only several threads on this topic of Audirvana playing through multiple output devices, the most recent one being from 2019. In it, Audirvana support replies that “In fact the feature you are talking about is the multi-room audio which is not available in Audirvana. We had several request about it and we don’t forget it but we need to prioritize the development of feature and this one is not our priority for the moment.” So I suppose that is still the case.
…at least for the legacy Audirvana product. That is why I am curious if the current one-time purchase and subscription versions of Audirvana might be capable of outputting to multiple devices.