The Kontakt player in Sibelius was developed for Sibelius only. GPO was made by a different company. As I understand it, licensing prevents them from opening up Sibelius for other players (and it sure has something to do with the fact that they want to sell their own Kontakt Player Gold).
right. You do NOT use the komptakt gold player that comes with sibelius. You can use that in addition to GPO I would guess...but for GPO you would use only the player that comes with GPO or full kontakt if you have it.
This is explained in detail in many other threads...search for them. Bottom line, Komptakt does not have all the capabilities that the GPO player or kontakt have. So you have to use either the GPO player or kontakt standalone with sibelius to use GPO.