I have done a project in Sibelius, exported it in midi, and opened it in Sonar. I then opened an instance of Aria and routed all the instruments accordingly (GPO4), and all played back fine - except the sounds are more like a Casio watch than the quality I heard on the demos. I know that EQ, reverb, etc all make a difference, but the sounds aren't close to what I heard when I bought them. I understand that they would need to be tweaked, etc., but does one have to be very adept at mixing to set them up to sound like the demos, or am I missing something obvious? Shouldn't we get pretty decent sounds even just "out of the box"?
There are 2 things that will improve the sounds. The first is to ride CC1 (modulation) throughout the piece for each part. CC1 is never a set and leave controller as this will make the sounds very static and boring. The sounds use a flex envelope which will vary the timbre as well as the volume as you change from soft to loud.
The 2nd thing is variations in velocity which will change the attack for most sounds.
These 2 things will make the biggest difference in the sound. There are other controllers which will fine tune the sound for even more variation.