hey man, let me be the first to encourage you to load up 33 instances of omnisphere in a properly load-balanced Vienna Ensemble Pro host (running with cubase) so you can really take advantage of that awesome horsepower you invested in. Vienna will outperform the same vsts against any mainstream DAW so if you want to set cubase free… kill the asio guard, and only use vienna in your vsti rack. For Steinberg being the originator of the entire VST format, their software IS surprisingly bad at hosting 3rd party instances of the instrument plugs; which is why everyone in the composer community (and some of us in pop now) use vienna.
not sure which OS you have but check into killing the HPET, killing redundant video card background processes, ENABLING hyerthread, DISABLING c-states and throttling… google “UNPARK CPU CORES”… a NICE little app is available to download that will easily go into deeeep windows reg-level land and UNLOCK the full power of your CPU. IF you need more info say the word.
Also you should know that Windows 10 has a known issue with managing higher levels of DLLs in active memory which could be giving you some weirdness. Consider testing out a quick Windows 7 (lean) build with cubase and omnisphere to see different results (I’ve built 4 or 5 windows 10 DAW workstations for other producers, but personally I still use an older version of 7 with certain updates removed that allow for better pro-audio realtime latency.
ONE other thing to check… if you are bussing/routing those VST instances through group audio channels (to stay organized like we do), try sending the VSTi audio output DIRECTLY out your hardware outs to test the performance. I noticed that CUBASE chokes hard whenever I have multiple layers of routing and on my active VSTi templates, I do route everything directly out and its a MEGA difference in snappy performance… of course in the mix or post stage, I’ll have complex routing for days… but definitely printed audio by that stage.
Good luck man. Hope something helps.