I don't know of any solutions, but I think i can tell you why they are CPU hogs.
At least for me anyway.
I run Cubase 9 with BIAS FX and BIAS AMP 2. I like to use AMP 2 within FX so I can use the FX with the nicer sounding amp models.
Turns out the BIAS plugs only seem to be optimized for 2 thread operation, so it pegs my first 2 CPU cores, while my other 2 physical cores (and 4 hyperthread threads) don't do squat. Total CPU usage will be less than 30%, but core one and 2 are pegged out and the VST engine is overloaded due to the plugin.
I'm using an RME UFX II. super stable drivers. I7-7700k, one of the fastest single thread CPU's out there even still (just barely slower then the 8700k). I also have it overclocked to 5.0ghz (stock is 4.2).
If i run one dual tone which means 2 total instances of bias amp 2 within Bias FX, at a 128 buffer, VST engine goes to 80+ percent. It's absolutely ridiculous.
You could have a $2000 CPU (i9-7980xe for istance) and still peg out your VST engine because of this plugin.
I isolated it to AMP 2. It was fine with any of the included Bias FX amps. When running 2 instances of AMP 2, the same effect occurs.
I am going to start a new thread about it, but thought I would post here in case you missed it.