Thanks, Brian. I use a USB cable. Spoke with McIntosh tech support. They , of course, referred me to Apple and JRiver.
That's unacceptable in my opinion. Your pre/pro is an exceptionally expensive piece of hardware that includes USB as an input. Either it's made to work with modern Macs and Windows machines, or it's not. They *clearly* have a driver for Windows. Is Mac supported? If so, they should be able to make it work. Macs are mostly pretty easy on the audio side. They conform to the USB 2 Audio standard (different than USB 2.0 data; this is an audio spec), so they mostly just auto detect almost every sound card or USB audio source.
This is clearly not a JRiver problem because Audio MIDI setup is an Apple utility that shows the sound cards on the system and the rates they support. JRiver isn't involved. Apple really isn't involved either unless audio support is broken. You can hear sound, so audio support is working. I assume it works with no distortion or anything weird happening.
I noticed that in my midi setup in includes "Soundflower 2 and 16 ch." setup. Apple tech support said this is a third party app. from Rogue Amoeba. I don't know what it is but it allows 192/24.
Sound Flower is a fairly well known piece of software that allows you to do unusual things like routing Skype calls to sound recorders, and all kinds of other audio trickery. It's not normally needed for audio playback. I would wonder why it was there. In fact, if I wasn't using it, I would want to uninstall Sound Flower. That would be one more thing off the list of things that might be wrong.
Finally, you asked about playing your 24/192 content that you downloaded. JRiver can do this for you very easily by resampling it, on the fly, and sending it to your pre/pro as 24/96 audio. All you have to do is configure the Output Format area to down sample anything above 96kHz down to 96kHz. See a screen shot and some info here:
http://wiki.jriver.com/index.php/Audio_Setup#Output_FormatChange the values of the items under Sample Rate. All items greater than 96kHz, change to Output 96kHz.
Good luck to you.
Brian.