HI,
I am on an Imac Catalina 10.15.7 and Sibelius 8.6.1 and playback is very bad because of continuous crackling (impossible to listen to the files). Moreover on the biggest files like Ark Pandora and Cathedral there's an untuned percussion that pounds away octaves from beginning to end without being written on the staff (you can see the key moving in the Spitfire plug-in.) The sound I hear in the Adagio for strings (the file with much less crackling) is AMAZING and sure what you are doing will be game (life??...) -changing for composers. Are these issues due to my MAC version (my Imac id too old to upgrade) or to not having Sibelius Ultimate ( I can upgrade if it needs). If these issues are fixed, I will certainly preorder the BBC CORE version and many others to come.
keep up this miracle!!!