Thanks so much for the replies! So, my Nighthawk router has USB inputs, which is good. I attached my USB drive to one of them, but can't see the contents on any of my PCs or Macs...
It turns out the Nighthawk won't recognize exFAT formatted drives, so I have transferred all my music files to an internal hard drive, used a "portable program" to reformat the USB drive to FAT32 (so both PCs and Macs will see it), and am now waiting for all 1.3TB of music files to transfer back onto the FAT32-formatted USB drive.
Is there a "trick" to getting JRiver so "see" the new NAS as the library location? When I say "browse", it only shows me local/attached drives.