The new 16 core Mac pro is crippled with 6 instances of U-HE Diva playing 8 voices each.. too much for single core load so it can only load 6 and leave all the other cores free.. it's the single core performance that is at fault here.. My iMac pro gets 6 also, yet my MacBook pro gets 15.. yes an 8 core MacBook pro gets 15 x 8 voice divas all playing back without logic overloads, vs 6 in a mac pro configured to about 14 grand.. There's a large topic at gearslutz explaining it all (the last 5 or so pages are the ones to read about this from memory), but basically OS X is not allowing the Xeons to keep a steady all core turbo speed and drops below Intel's actual rated speeds, whereas Windows is letting them perform at their maximum. For example in my iMac pro, i get 12 divas in Pro tools/bootcamp vs 6 in Pro tools/Mojave. It's a power limit issue in OSX and we all hope it gets worked out. The reason the MacBook pro gets one per available thread in Logic is because there is enough headroom left over after each one, to put the next one on.. With the mac pro's, the reason they can only play 5 or 6 is because even though those first few instances can be loaded on one core each, every new instance adds overhead even to previous cores, just slightly, but there is no headroom left in the single core performance so it flakes out much quicker. The 9900K gets like 20 or something.
Yet, with omnisphere, there is a demo of the new mac pro playing 80 of them and all 16 cores/32 logical cores getting hammered to the max. So really, it's only U-HE synths that seem to not be able to be fully taken advantage of on the Xeons.. I have other heavy cpu synths and I can use them all.. just not Diva.
All the Arturia stuff is fine, Dune 3, the legend which sounds *amazeballs* used about 1/5th the cpu of DIva's moog filter mode. Try the legend, you will love it.. Only 8 voices but he used an AVX trick to get it to perform like other synths with one voice!