Hi all. I’m new to this forum and not yet a PSA customer, but I do know Macs and digital audio. Maybe I can help a bit.
If you are using an audiophile music player on Mac, such as Amarra, Audirvana+, BitPerfect or Fidelia then for the most part the settings in Audio MIDI Setup do not matter. This is because the audiophile apps are all capable of independently selecting your DAC as their output device and setting an appropriate sampling rate. For the DirectStream you would want to configure the software for bit-perfect output, with the output sample rate changing automatically to match the track being played.
The settings in Audio MIDI Setup are only relevant when you have audio from multiple apps being mixed in the OS by the CoreAudio subsystem before the result is sent to the sound hardware. CoreAudio will do on-the-fly sample rate conversion (SRC) so that audio streams at different rates from different apps can be mixed together and output at the rate you’ve specified.
iTunes - when used on its own - will take note at launch time of the current Audio MIDI settings and will subsequently perform its own independent, higher-than-default quality internal SRC and volume control before passing the audio out for mixing and playback. So if you want bit-perfect playback from iTunes by itself you have to quit it, set the playback rate in Audio MIDI Setup, then re-launch iTunes. Repeat every time you want to play something at a different rate.
Amarra, Audirvana and BitPerfect can all be used as companions to iTunes, where iTunes is your music library manager and primary user interface but the audiophile app takes over the role of actually playing the audio. I currently use Audirvana in this way because my Metrum Octave DAC performs best with high-quality upsampling (44.1/88.2 -> 176.4 and 48/96 -> 192) and I like the iZotope SRC. But if I end up taking the plunge with a DirectStream, I’ll switch to using BitPerfect.
BitPerfect can only be used as a companion to iTunes. It does absolutely nothing if you’re using some other player. It can do SRC but only with the free CoreAudio and SoX libraries. Its big claims to fame are (a) nearly-invisible operation, (b) automatic sample rate switching for bit-perfect playback and © iTunes-compatible support for DSD audio with DoP output. No FLAC, but you can batch convert FLAC to ALAC using XLD and then you’re up and running in iTunes world. For most people, this is the least-complicated way to get everything you want out of a Mac and a DirectStream DAC.
Audirvana, Fidelia and JRiver also function as standalone players. I have not used JRiver, ever. Audirvana has no library management of its own: if you’re not in iTunes-integrated mode then you’re manually managing audio files in the Finder and creating playlists. Fidelia has pretty basic library management but mostly relies on using your existing iTunes library in a read-only mode. For bit-perfect playback to DirectStream, any of these players should be able to do the job and won’t care about Audio MIDI Setup.
Clear as mud?