IMO controls are genuinely hard in AVE/VR studies. There isn't an obvious "inert" placebo, no light/sound removes immersion, random flashes or audio still affect arousal, and even "wrong" frequencies can entrain.
VR-only controls help, but don't isolate sensory stimulation. That's why many early AVE studies use pre/post designs and treat results as exploratory rather than definitive.
As for binaural beats and isochronic tones, it's all about using the right frequencies, how you transition between them, how you combine tones or beats with other music or sounds, the carrier frequency, how you synchronize lights with the tones or beats, and so on.
VR-only controls help, but don't isolate sensory stimulation. That's why many early AVE studies use pre/post designs and treat results as exploratory rather than definitive.