The roli seaboard works all fine with Halion 6 !!
I experimented with it for some time now, working on a 5dim instrument, with macro and luma code, and created about some 30 new sounds with ALL the 5 dimensions.
Halion offers you to do it all, although you have to learn some tweaking parameters, like offsets in the matrix to have the cc74, and after touch working the way you want it to 
I might do a video soon on me creating a sound from scratch, for my library with the roli, but couldn’t find the time yet. If I do, I’ll post the link to it here.
One thing important is to set the MPE on off in the Roli dashboard, and multi channel to on (1-16), pitch to 24. If not cc74 will not work properly (touches on the upper parts of the keys will not soud like those on the lower parts)
In short… Halion and Roli work very well. Of course, direct integrated mpe support would be welcome (no need to create the 16 instances and mpe protocol supported) but maybe in a future upgrade?
LuLu