Are computerized sounds Pacman, hmmm i sample in the same Sibelius software, and i use East West samples to make a better sound of the midi, i dont have recordings with real instruments at the moment.
The best sound libreries i can recommend you are:
East West
Reason
Giga Studio
also, the sibelius real sounds, garritan personal orchestra or if you want to upgrade a little the midi, the Hyper Canvas has a nice midi sound.
This is current software i have to sample midi, and its a little heavy...
East West Quantum Leap Symphonic Orchestra Gold XP (140 Giga aprox)
East West Colossus (40 Giga aprox)
East West Symphonic Choirs (30 Giga aprox)
East West Stormdrums (4 Giga aprox)
Grandioso Bosendorfer (4 Giga aprox, Just pianos)
Hardcore Bass (3 Giga aprox)
Superior Drummer 2 (18 Giga aprox)
Abbey Road Modern Drums (7 Giga)
Steven Slate Drums (720 MB)
If you have midis and want to make a better sound for the midi, you can use the FL studio with the .dll files
i used to do that in the Guitar Pro times