Hello, I've had GPO for quite a while now... and while I have been involved in this community I have only used GPO and Sibelius 3 as a notation program. It seems to me that a lot of these other pieces have things that mine lack... I have always used point and click to make music in Sibelius (no keyboard, for some reason when i write with keyboard, there is atleast a half or full second delay with GPO from where it is actually recording making it impossible to use the keyboard to write songs...) i don't have a sequencer or a sequencing program, things such as timpani rolls, french horn rips, pitch bends, etc. are impossible (it seems) to do with just Sibelius 3... This may seem dumb or odd, but I am wondering what programs or hardware I need to take my music to the next level... or if there is a way to work Sibelius 3 to fix some of the things I mentioned above.
Easiest thing to do is to upgrade to Sibelius 4 and get the Sib/GPO crossgrade. All your articulations, dynamics, crescendos, etc., will playback. If you have very specific questions, you can post them - but to answer your general question, I'd move to Sib. 4.
Another option is to save your files as MIDI files, then import them into Overture SE which came with GPO: it has sequencing controls that you can use.