Huge spike in first core when using NI Drummer mixing presets

If I use any of NI's drum instruments (Abbey Road, Studio Drummer etc) the first core spikes dramatically if I use any of the mixer presets. This is OK in a light project, but once the project starts getting heavier then it seriously affects things and the first core spikes into the red (all other cores showing relatively low activity). 

The thing that confuses me is that I have Kontakt set up to use all 6 cores in the options. Yet when using as a vst in Sonar, it doesn't appear to spread the load of those mixing effects at all. 

In fact first core spiking seems to be an ongoing problem for me with Sonar in general. I have changed the relevant parameter in the config file as others have suggested. Yet still, that first core....oh man!