Hi Mike.
I have had quite a few issues with the new Synchronised SE libraries with Sibelius too, and have spent ages on some of them trying to get them to work as per my original VI Pro scores.
What i have found, is that sometimes, for what ever reason, things sort themselves out if you cut out the offending staves and copy them into new ones.
I found that it was mostly strings that where causing the problem, and if i added the full version of a specific library to my playback configuration (for example, if i added the full Solo Strings and used the VE Strings sound set), then the Solo Strings work beautifully and fully as expected. However, if i then added the SE versions of Orchestral, Chamber and Appassionata to my config and for those libraries use the Special Edition Plus sound sets in my config, then i could have problems with Sibelius selecting the wrong instrument in the channel mixer. And dynamics and articulations could also get played incorrectly in this example too.
Like you, i've also had real trouble running the synchron version of my configutration in Sibelius without a load of pops and clicks and the CPU meters jumping of the scales, so its great to see that Andi and the guys have identified an issue with the Synchron Player that there working on a fix for.
I have to say that i can only imagine the work that's involved VSL's end to get there software to work with Sibelius, and i think that what they've achieved with the SE versions is superb, so i cant wait for the new sound set to come out with the Dimension strings special editions 5 so i can see if i prefer the VI Pro or Synchron versions...as i cant help feeling that my wallet is going to take a hammering!
Kindest Regards
Paul