I did some experimenting with background horns on this. I was very much surprised to hear how well GPO's French horns blended with a basic jazz quartet. I used 5 different instances of the f horn and applied jazz harmonies on them. Whether this song is good or not so good will certainly be subjective, but I think that the way the instruments blended is a very warm sound, at least to me.
I also used JABB flute and E. Piano.l
Please give a listen. Jay