Multiple Instnaces of VIs vs. multiple MIDI tracks targeting a single instance?

[kirkbross]

My typical process is to create an Instrument track with Omnisphere (for example) and then create 8 MIDI tracks to send to the MIDI channels 1-8 of Omnisphere. i.e. 8 different sounds playing 8 different parts from a single instance of Omnisphere.

Is this the best practice in terms of computer resources or is it better to create 8 separate instrument tracks, each with an instance of Omnisphere, and have just a single sound in each one.

I ask because a friend said if they're all stacked in a single instance, they can only use one CPU thread.