FWIW I found something of a kludge work around for using one WSJT-X with other instances of JTDX.
Stop all instances of JTDX and JTAlert. Start one instance of WSJT-X and JTAlert for WSJT. Start two instances of JTDX and JTAlert for JTDX. The first instance of JTDX will not work with JTAlert but the second instance will (and a third and a fourth). I've only had this running for a couple of hours so maybe I'll run into a problem sooner or later.
I have my 1st instance of JTDX minimized and getting it's audio from an unused input source to keep the load down. My computer can handle the extra overhead but slower computers might not.
There is probably some fatal flaw with this idea!??
73, Jay K0GU