Is JRiver still the best software?

JRiver when properly set up, and with Redbook or HD sources, will definitely "knock you out" in comparison to Apple Music, if the rest of your system is even basically adequate.
Why are you resorting to a MIDI protocol?  This likely relies upon your computer hardware sound card for a conversion that you will want to entirely bypass.
I assume you are using Macbook's USB Out to Mcintosh 50 Digital In.  Go to Jriver Wiki and follow instructions for DACs with direct USB connection.  If your MaC DAC has a proprietary software driver, use it.  If not, under "Audio Output/Output Mode" select "Core Audio".   Then follow the other setup recommendations in the Wiki.
That should get you started and may also solve the data display problems you mentioned.

Your DAC appears to take the direct PCM digital stream of any resolution and upsamples it to 32/196, but the incoming preconversion bit/sample rates should be displayed on your screen.

You will also find that JRiver completely supports appropriately configured metadata.

@sandstone I appreciate the input - gave me the trail of breadcrumbs I needed to sort things out.

It wasn’t actually quite that simple; had to uninstall and reinstall JRiver before I was able to bypass the MIDI and get the settings changes to work. Tested it briefly this morning and verified files run in native resolution. FWIW, the C50 DAC doesn’t upconvert, just automatically adjusts to incoming bit depth and frequency.

Still haven’t been able to obtain the metadata; JRiver doesn’t seem to know where to find it. Maybe I just have to leave it running the search function for a few hours. Haven’t spent that much time on it and it’s not a huge priority anyway.

Thanks again!

FWIW, the C50 DAC doesn’t upconvert, just automatically adjusts to incoming bit depth and frequency.

I'm sure others have different opinions, but I never like up-converting Redbook CD or lower bit rates to something higher.  It is a DSP process that attempts to put additional time slices in between the 44.1kz sampling data.  It may create a "smoother" sound, but it's artificial and I find that I like listening to the original 16/44.1 sampling better.  It has more impact because the timing is closer to the truth of how the waveforms are presented rather than a theoretical conversion to a higher sampling rate.

 

@auxinput I fully agree, which is why I’ve been chasing this irritating fly in the ointment for so long. Moreover, the native file is how the artist released the material, and one would presume that’s how it was meant to be presented.

It also turns out I spoke a bit too soon about everything working correctly after my quick test. Hadn’t looked at the output data carefully enough. Turns out that while JRiver is now presenting the native frequency (44.1, 192, whatever), the bit depth is fixed at 32. This is confirmed by both the audio data window within Media Center 27 and the C50 on-board display. The data window shows the native data and the output data. The output data matches the C50 display. One example was a Linn classical piece with native 24 / 88.2 and was running at 32 / 88.2. It sounded quite a bit better than when both bitrate and frequency were upsampled, but still artificial.

I’ve posted on the Media Center support forum to see if I’ve missed setting a software switch somewhere; no replies yet. The Apple support forums aren’t especially helpful other than to say that the MIDI interface will only output at whatever bitrate and frequency combination is selected in it. I knew that already and am trying to bypass it as @sandstone suggested. This whole computer audio thing is very frustrating. All I want to do is play digital music in native format. The only device I have that will do that is my MVP-881BR. So far, it’s the hands-down winner in both convenience and sound quality.

 

@effischer ,

Glad that you're making progress and have experienced more of the capabilities of your excellent Mac C50!   Just a couple of questions/ suggestions:

Have you by chance downloaded and installed the software drivers and setup instructions from Mcintoshlabs.com?

Use a good USB cable (e.g. Belkin Gold) to connect  your computer to the USB port on C50. 

Then, look up
"USB Audio Windows Driver A Version 2.0 Installation and Operation Guide"

The driver install file is located right below the Guide.

Once this is installed, restart JRiver which will recognize and list it as a McIntosh-specific Asio driver option, that you should select.(Tools/Options/Audio Device).

This Centrance (third party) software is great stuff, btw. 
 

Then look up and follow

-- "McIntosh 32/192 PCM DAC, Preferred Settings to Play all File Types with JRiver Media Engine 20 using a Windows 7 or 8 Computer" --

This file is for the C52 but it steps you through what you also need for your C50.  

You should now have direct control over all the flexibility that the C50 DAC will allow.  Try selecting AUTO when given that option.

-----

As for metadata mgmt,  

Go to first principles...Try just ripping a single Flac file, store it locally on your computer, and use JRiver's Library management tools ( well documented on JRiver website) to define the file path to your file as a Library, then set that as your active library.  Save. Then it will persist when you log off.  You can then load as many other files into this path (Now a Library) as you wish. Or create and load other libraries. A Next step is to then use DLNA protocol to define any file set on your network and activate that as your Library for JRiver to manage.

Apologies if you are already beyond this level of detail.  Just let me add that Using  ASIO protocol and the USB asynchronous port is the recommended connection for your DAC, as it is with many other higher end DACs.

Hope this helps, good luck.

Sandstone