I've just discovered that the sustain / legato control has a very noticeable effect on the timbre of the Project SAM French horns. Is this intentional? It makes the horn sound tinny - almost muted. Mixing slurred and non slurred notes (using the legato function) makes a very unnatural sound.
I ran into this using Sibelius6.2 + GPO4. It's less noticeable with Finale + GPO4 (depending somewhat on the "Human Playback" settings), but it is apparent just using the stand-alone Aria console so I know it's not (just) a Sibelius problem.