Volume difference between Audio APIs

Fair enough- compressor behavior does get increasingly unstable as attack time approaches 0, and that goes for all compressor designs. You noted previously that other real-time compressors don’t face this issue:

I would be interested to know which compressors you are referring to as most commercial compressor plugins give you a minimum attack time of 20ms, which is much higher than our minimum of 0.1ms. If there are any compressors you know of that go as low as 0.1ms without introducing clicks with high energy input I would like to test them against the FMOD compressor.
As for the pops and clicks, that click is the n milliseconds of raw input before the compressor clamps everything down, creating a transient. If you can distincly hear that, that is a sign that your compressor is being overworked and you need to offload some of that peak handling somewhere else, such as one of the methods suggested above. I think if you do that, you will find that the FMOD limiter and compressor will be more useful for you.