I just experimented with this and when I drag a list of files to the player JRiver uses the folder sort. Normally your computer will sort files by name, so dragging the folder to JRiver causes the files to populate the playlist sorted by name, which is probably not what you want. However, if you you change the Windows or Mac setting to sort the folder by file date, you'll get the tracks in disc order because that's how they were created during the rip. When the folder is sorted by date, dragging it into JRiver causes the playlist to be populated in disc order. At least that's what happens on my Windows computer.
I listen to a lot of classical music and JRiver has been a godsend. Before JRiver I spent a lot time looking for the physical disc I knew I had, because I couldn't remember how I'd filed it. JRiver solves a huge problem for classical music libraries. But if you really don't want to import your collection, reconfigure your ripping process to start the file name with the track number, as has been suggested. Then you don't have to change the operating system's default of "sort by name".