Hi, thanks for the feedback. I checked Audio Device and it only lists the laptop speakers, the default Core Audio, and just now my miniDSP device plugged into a USB port. Both exclusive use and integer are unchecked. It turns out, via a post on Audio Science Review, that JRiver requires an external utility in order to connect to an Airport device (something to do with DNLA or lack of). So I used Airfoil by Rogue Ameoba, which lets you 'connect' an app to a device. This does the job.
By the way, the original playback issue (sample rate) still occasionally rears its head, no idea. Try again a time or two and it usually starts playing. Now to try to figure out why it only imported a small fraction of the Album cover art from my Itunes library
Have to admit, the learning curve on this piece of software is a brick wall. Seems like it sure could use a user's guide. I mean REW has one, and it's free