I posted it in another thread, but here's my quick impression so far:
Acid 9 needs a patch quick. I have a bunch of older projects that use Waves regular VST plug-ins (x64) and some of them simply crash the application. It seems the changes they introduces were mainly focused on support of VST3, however the regression testing for older plug-ins was spotty. I suggest you do not remove the v8 and use it to complete the unfinished tracks, otherwise you'll have to reconfigure, re-apply the VST3 plug-ins for the v8 tunes to work with v9. Also, the icons bar in v9, the one below the menu bar is shifted lower and off-center, so only 70% of icon is displayed... some graphical glitch. QA needs some improvement in the Magix shop. When Sony owned the product this was never an issue with back-wards compatibility.