That’s what I did:
I’m using HALion SE for Trumpet & Piano
I’m using a VST PlugIn called Trilian for Double Bass
I’m using a VST PlugIn called EZDrummer for drums.
To find out a work-around for my slash problem (I’m still convinced that slash-notation is NOT possible if you use a 3rd party VST and not GM or the Yamaha) - so I added another drum set (basic) which I wanted to assign to HALion SE on Midi Channel 3 -> screenshot1
I opened HALion and added a GM JazzKit on midi Channel 3 -> screenshot2
I opened my HALion Endpoint Setup dialog
…and look what I got on Midi-Channel 3: a number ‘6’ - I can’t change it, I can’t assign it to the drum kit -> screenshot3