I had exactly the same trouble with my 4790 and was getting spikes with one instance of Omnisphere. Just playing a simple analog pad.
I found that turning off C steps in the BIOS fixed this. I then proceeded to duplicate the same track until I had 20 copies and on playback the real time peaks were gone.
I stopped at 20 satisfied that I had found the issue. Haven’t seen a real time peak since.
C steps is part of my ASUS boards BIOS set up.
It’s to do with energy management and as someone posted above these things should be turned off in bios.
Go into your BIOS and find your way to the CPU features.
Google the names of the different features and if they sound like power management/ throttling features disable one by one and retest between each change.
Good luck!