Hi Peter and welcome to the community.
The way to do it is not to use JRiver and ASIO using USB (presumably from a PC). As you become familiar with this forum you will find over and over again that the best sounding connection to the dCS DACs is network. So you need to have all of your files including the DSD ones available from the same network source. To do this you need to copy the files to network storage . A basic home NAS from QNAP or Synology for example will work well for this purpose. You also need to load UPnP server software on to the NAS. For ease this should be Minim Server, see FAQ:
Once set up ( it is not difficult) and with both the NAS and the device running Mosaic connected to the same network ( use inexpensive certified but unshielded CAT 5e or 6 ethernet cable for the NAS/Bartok connection) when you open UPnP on Mosaic all of your music files, irrespective of file format, will be listed and be ready to play. MinimServer allows you to list and select them on Mosaic in various permutations as you wish e.g. A-Z album title or by genre or by artist or year of release etc.
You will also find that no matter how good you think JRiver/ASIO/USB sounds there is a lot more there. I remember when I made the same transition and which I described as " a whole new listening world".
I hope that this is helpful.