How to do this

In C 6.5 I create the MIDI tracks using Halion 4 usually these are Drums, Bass , Piano, Organ etc.
There is one instance of Halion 4. How can I export the one instance of Halion 4 into Mono (Bass) and Stereo ?

not sure what you are trying to accomplish - do you mean bounce your midi parts stereo drums, mono bass and stereo everything else into your project ?

or export the bank of programs for use elsewhere with all samples? not on H4 but in Halion 3 there is a pull down window if you right click in the lower right hand side of the gui and select “export bank with samples” ( or something very similar)

or do you just want multiple routings into yoru project - to do this just click on the the little box with the arrow in the VSTi pluggin window in cubase and it will have a drop down menu where you can select multiple output channels ( this will automatically create mixer channels in your project). from there you will need to go to halion and route each program to the desired output.