This is on a 12 core MacPro trash can with 32gb ram and a UAD Apollo.
This problem is there with other interfaces as well, I have tried a FF800 and the internal audio, same terrible performance.
Cubase with no project loaded uses around 80% CPU, with a single track with Diva using the default patch it uses 210% CPU.
The equivalent figures in Logic X are around 2% and 18%.
Any ideas what might be going wrong?