I use the ToneBoosters Eq v4 as well, to eq my headphones. I asked TB support and Jeroen reply was:
“… Indeed, as long as you use simple EQ-ing, they have the same effect. They will make a difference though as soon as you enable dynamic equalization or non-linear filters. In both cases, increasing the input gain will drive the signal harder into the dynamics and/or non-linear filtering modules, respectively, and you can compensate for that using the output gains.”
I normally use out gain for oratory, autoeq and speakers to reduce level when needed.
Hope this helps!