I also read your first post as you having trouble turning off crossfading. Jim did answer that.
To use two instances of JRiver you need to go to Tools > Options > General > Advanced and check "Allow multiple instances to run at one time." Then you can launch more than one JRiver program. You do this by clicking your shortcut or icon that started JRiver the first time.
Rather than use multiple instances, JRiver now allows you to create Zones with separate audio device selection for each Zone. This may be easier to use.
http://wiki.jriver.com/index.php/ZonesUse View > Split View and show 2 or 3 views. This will let you use one view for speakers and one for headphones. You can also lock the view. You might want a 3rd view for showing Playing Now.
You can use the same audio device for each zone, but specify different output channels to route to speakers vs headphones. What audio device do you use?