I thank you Anton,
for your comments.
I have another question for whom can answer it : if I decide to purchase Opus, I will use the library with Halion.
It seems that the Performance Tool is not impossible to use with Halion, so this is not the issue.
And Halion converts gig files quite well, especially in the department of keyswitches, but noticeably less well when it comes to more complex programming, like xfades between layers. I unfortunately am not an expert at programming, and would not like to spend 2 years tweaking the library, so my question is :
is Opus mainly made out of "basic" k-switched programs, or does it involve more sophisticated programming features -which might be a problem conversionwise ?
I would also appreciate comments from people like me (I mean Halion users) who took the same boat and can report good and bad experiences.