Horn choirs (and most other such) tend to be an acquired taste.
It's also darned tough to get software French horns to sound like the real thing -- the brightness they can have when needed, and the wonderful nuances they can manage -- so one needs to listen with that in mind.
Personally, I don't know if I'd even attempt something like this in GPO. Maybe supernaturally-eared beings like DPDan can pull it off, but mere mortals such as you and me?
I'd probably bunt and run, and reorchestrate for full brass...